I tried to install Mandrake 9.1 on the same system as WinXP. I used Partition Magic 8 to format the last 10 gigs of my hard drive (ext3) and then I used the "add another operating system" option, which apparently sets that partition as the active one. After installing Linux, however, I could not get back into Windows XP. Can anyone tell me what I did wrong and how to avoid doing it again? (I ended up reinstalling Windows).

You don't need to use Partition Magic to install another OS. The best thing to do is:

1 - Install Winslow eXPeriment in the first partition. If you install using NTFS, you won't be able to write to it when you boot into Linux. I highly recommend FAT32 for a dual boot.

2 - Go into your bios and make sure the boot order is set to "CD Rom first". Place the Mandrake 9.1 CD 1 in the drive and reboot. Mandrake has great tools for creating Linux partitions, don't use PQ Magic 8.0 for that

I'm already using NTFS for my first 4 partitions, followed by 1 FAT32 partition and 1 ext3 partition. Does that seem alright?

You will need to create a swap partition as well. All you need is free space on the hard drive for Mandrake to use. Free spac can be obtained by resizing or deleting current partitions. The installer will then let you format and partition the free space, or it will autoformat and autopartition for you. You can select your existing ext3 partition for install, but you will have to further partition it so that there is a swap partition available. Make sure that you install the boot loader in the master boot record to overwrite the windows boot loader.

..........also - I wouldnt mark partitions as "active" in advance using Partition Magic - its sufficient to install LILO or GRUB to the MBR and then create the appropriate entries in thier respective config files if they havent already been done so - often LILO or GRUB will automatically recognise a Windows install and configure the config file appropriiately - if not its usually a straightforward matter of adding an appropriate entry for Windows.

Not necessarily true. Some distros come with ability to read and write NTFS partitions. I am not sure which ones come with it included... I think kernels 2.4 and up support it with additional and better/more reliable support being developed.

Edit - Found the NTFS project site goto: http://linux-ntfs.sourceforge.net/

that is what from the ntfs site, and that has been the state of write to ntfs for a while now....and as they state its extremely dangerous, so basically what megaman said is true, cause your actually going to screw stuff up after a while if you use the write support...so all in all it more or less is just safe to use read rather then both read/write...

Ok, so maybe I skim read it

Okay, but that doesn't really answer my question. I've already got the first partition formatted to NTFS. Why would Linux need to write to that partition? I have one ext3 and one fat32 partition. I'm just trying to use the ext3 for Linux and that fat32 to share between OS's. Right now, I'm basically trying to figure out if this can be done with my current configuration.

I see no reason why it couldn't be. but you will have to resize the ext3 or fat32 partition to make room for swap if you don't have room left on the hd. The mandrake installer will let you do it. Basically no need to set up the partitions in advance for the mandrake installer.