Goofball_77: You said that you want to let Windows handle the selection of the OS. Won't happen. Windows won't even acknowledge the existence of Linux, even though Linux tries to play fair. If you install Windows last, then you'll boot up in Windows. You won't even get to use Linux (unless you use something like a Knoppix CD to intercept the boot process before Windows gets to it).
From what you describe of your hard drives, this is what I *think* I'm hearing:
You have two hard drives, both in your computer at the same time. One contains Windows XP and the other contains Mandrake 10.
The question is, which hard drive contains which? There is a definite order to the hard drives, depending on how they're cabled together. Let me explain, and then I'll say why this is significant (I'll explain terms afterward):
1st hard drive = hard drive on Primary IDE channel with jumper setting "master"
2nd hard drive = hard drive on Primary IDE channel with jumper setting "slave"
3rd hard drive = hard drive on Secondary IDE channel with jumper setting "master"
4th hard drive = hard drive on Secondary IDE channel with jumper setting "slave"
The "Primary" and "Secondary" IDE channels are, for newbie purposes, the cables that connect your hard drive to the motherboard. If you open up your computer, you'll see these flat ribbon cables. Modern computers generally have two of them, connecting to the Primary and Secondary IDE channel on the motherboard. Each ribbon cable can connect to two hard drives. (A CD-ROM acts like a hard drive.) So you can have a total of four hard drives / CD-ROMs / whatever in your computer.
(For the record, the 1st hard drive is referred to as "/dev/hda" in Linux. The 2nd hard drive is "/dev/hdb", and so on.)
You don't necessarily have all four hard drives, of course; your two hard drives might be configured as "1st" and "3rd", for example. Note that under Windows, the hard drives are assigned drive letters "C:" and "D:" etc. in order, ignoring any non-existent drives. This means that, just because your drives are called "C:" and "D:" under Windows, they aren't necessarily 1st and 2nd; they might be 1st and 3rd, or 2nd and 4th, etc. You have to actually look inside your computer physically to find out. (Linux DOES differentiate, and if you have only 1st and 3rd, you'd have /dev/hda and /dev/hdc but no /dev/hdb.)
Most computers are set up to boot from the 1st hard drive, unless you've changed your BIOS settings. (Careful: some BIOSes refer to this as "hard drive 0", and "hard drive 1" is actually the 2nd hard drive, something that wasted hours of my time on a wild goose chase.)
Suppose Linux is on the 1st drive and WinXP is on the 3rd drive (my recommended config --I'll explain later). When you boot, you boot from the 1st drive and go into LILO, the program that lets you pick the operating system. (There's a substitute for LILO called GRUB, but Mandrake 10 uses LILO unless you ask for GRUB.) This LILO program itself is not on any particular partition, but is in the MBR (Master Boot Record) of the 1st drive --sort of like the margin on the inside cover of a book, rather than any particular chapter. If you ask LILO to boot XP, fine, it goes to the other hard drive and XP starts running. If you ask LILO to boot Linux, that's okay, too; it goes to the 1st hard drive where the Mandrake partition is and starts running.
Now, suppose Linux is on the 3rd drive and WinXP is on the 1st drive. When you boot, you *still* boot from the 1st drive. LILO is still loaded on the MBR of the 1st drive, even though Mandrake itself is on the other drive.
This has consequences when you want to separate the drives. Suppose you say, "Well, I don't need Windows, so I'll just throw away this 1st hard drive with WinXP on it." Guess what? You can't boot Linux any more because LILO was on the 1st hard drive. If you keep the WinXP drive, you can boot XP, but there will still be LILO on it.
LILO has two jobs. One is to let you choose which OS to use. If you choose Linux, though, it has the additional job of actually loading the Linux kernel to get Linux up and running. That's why it's called LILO (LInux LOader). Keep this in mind for what's coming up next.
The point is, if you don't want Linux (well, LILO) to be in charge of booting, you have a choice! There are other boot managers, and one that I've used before and works well is SmartBootManager. Check out
This handy little program can be installed on hard drive, CD-ROM, or floppy, and is great for booting anything, such as working with old computers that cannot be set to boot from CD. (Yes, Smart Boot Manager is free.)
Smart Boot Manager can't *load* Linux. It can only transfer control of booting to whatever partition has your OS of choice, such as Linux. If Linux doesn't have LILO, it's still dead in the water.
What you need to do in that case is to install LILO *on the Linux partition*, not on the MBR itself. You had the option to do this when you first installed Mandrake 10 (although you've probably forgotten). You can still do it now, as follows: from the Main Menu button > System > Configuration > Configure Your Computer. (Then enter root password.) Boot > Bootloader. The default is LILO on /dev/hda. This means the MBR of /dev/hda itself (remember, "/dev/hda" is what Linux calls your 1st hard drive). To put LILO on a partition, such as /dev/hda7 or /dev/hdc1, select that actual choice from the drop-down menu. You have to know where you installed Linux. If you don't know, type "mount" in a console/terminal/shell and look for the line that says "on / " with a space after the slash.
(By the way, remember this boot config screen --I'll come back to it later.)
Assuming you've done this, LILO is now also loaded on whatever partition actually contains Linux. Then you can use whatever boot program you want, whether it's also LILO or whether it's Smart Boot Manager. You won't, however, use Windows because it will be a cold day in hell before Microsoft writes any software that acknowledges the existence of Linux. (Don't worry, that day will be coming soon, but not just yet.)
I hope this answers your question. If not, you better explain it a bit more. (Actually, a LOT more.)
Remember that boot config screen I told you to remember? It also has options for APIC, local APIC, and ACPI settings. You mentioned "no end of troubles" with Mandrake 10. These settings might help if it's a matter of Mandrake not working well with the hardware. That's anothet story, though.