so i got an acer lappy with linux(no idea which version) preinstalled. 120 giggs, divided into two partitions.
i proceeded to install xp. now the problem is, xp recognizes only one of the drives, which means, my other 60giggs has disappeared somewhere..nor do i know how to startup using linux..
wad do i do?

If the hard disk is divided in two partitions or more, Windows will only recognize Windows partitions (NTFS or FAT) and not the Linux ones. It probably won't even see them. Linux on the other hand will recognize ALL the partitions, including the Linux Windows one(s).
So, the other 60 GB hasn't disappeared, but rather it is formatted somehow for Linux, most likely. Infact, there should be more than one partition for the Linux; a root partition, a swap partition, and possibly others.

As to how to boot Linux, that's a good question. Is it not listed on whatever bootup menu you get, or does the machine boot straight into Windows?
Have you got any CD/DVD's with the machine, like maybe a Linux disk? Or maybe a Linux LiveCD you could boot and use to examine what's on the hard drive?

ye, it does not show me the drives Anywhere!
the machine boots straight to xp, and when i enable boot login, it just shows xp. no linux material was supplied
what can i do to access linux or the houdini drive?

Does this machine have two hard drives? If so, try going into the BIOS and changing the BOOT device order, to boot the other hard drive first.

Another idea may be to press F11 during startup, and see if you get a boot menu.

one hard drive
F11 no go

Well... That's quite baked

Have you got Highspeed internet? If it were me, I'd be getting a Linux LiveCD of some sort of your choosing, and have a look at the system using that.
I'm out of ideas as to how to boot the thing as it stands. If they installed Linux, and then installed Windows second, then chances are that as you can see Windows has overwritten the Linux bootloader, and worse case scenario, Windows has ruined the Linux installation, in which case (almost in either case) you will want to reinstall a new Linux on the machine. It would help to know what Linux is supposed to be on there, so you could download THAT version. That would be most helpful in repairing the installation.

As for dual booting, generally one installs Windows first, and then installs Linux, so that the Linux bootloader can be used to boot either OS.

EDIT - I just re-read your original post. When you installed XP, you overwrote the MBR, which means it erased the Linux loader.
You'll need to reinstall it, or find out what Linux it is so you can download it and fix the installation.

ok.
so tell me what exactly to download..and what to do with it?
then i will have one xp, one linux? or can i access either of the drives from either OS?

When you installed windows on a computer with Linux preinstalled, windows installed it's own bootloader to the MBR of the hard disk, which wiped out access to the grub menu that would give access to Linux. The Linux OS is still there, just not accessible because windows doesn't recognize other OSs (that's the microsoft corporate culture at work). It could be worse: windows could tell you that there is an unformated partition and offer you to opportunity to format it for windows, thus wiping out Linux. A careless response from you is all it would take.

So. Does the lappy have a cd or dvd writer? If so, download a Linux liveCD to windows, and burn it to cd. Most that I have tried have good hardware detection. My personal favorites are Knoppix, Kanotix, and PCLinuxOS.

Make a liveCD (you can also buy them for the price of a hamburger) and boot the liveCD. Run grub-install to write grubs first stage to the MBR of the hard drive (read the grub manual for specific commands).

Mount the partition that has Linux, and make any necessary edits to /boot/grub/menu.lst (have to be root to do that). Make sure the Linux entry is correct, then add an entry for windows (you can find examples of the entry in the LQ forums).

Then shutdown and remove the liveCD from the drive. Power up and you should see the grub menu. Test both entries to see that they work.

Download a Linux operating system that appeals to you. You'll hafta do your research there to see what you want. If you're new to Linux, one idea is Ubuntu (not my personal choice) if you have enough system memory to run it.

After it's installed to the partition(s) where Linux already existed, and the bootloader configured to boot Linux and XP, then yes, you will have two OS's, XP and Linux.

You will be able to read/access the Windows drive(s) from Linux, but as mentioned, Windows does not read or recognize Linux filesystems, so from Windows, you can only do Windows things (blah).

If you download Ubuntu, which comes as a LiveCD, or any other Linux which comes as a LiveCD, you just stick it into the CD/DVD drive and boot it up. It'll start just like Windows does, but it'll be Linux, and it will have a method of installing it to the hard drive.

EDIT - and yes, do like bigrigdriver said above

Ubuntu is a big, bloated OS, but if you like that, go for it.
I like Slackware, but some say it isn't a beginner distro. Do a bit of research, browse the forum, read the descriptions and reviews of some popular Linuxes, and download something

Sounds like your Master Boot Record was snatched by Windows XP. Usually Windows will take over the MBR if it is installed after Linux, Which will make:
- Linux unable to boot
- Windows will not see the Linux drive.

I say start over and Install Windows again as your first OS. Then pop in a Linux Installation cd. Usually the Windows partition will be detected during the Linux installation and will set itself up to boot both Windows and Linux.

Download the live CD and burn it to a cd/dvd
Boot from the live CD

Go to the Terminal type

sudo grub

at the grub promp type

find /boot/grub/stage1

it will come back with some thing like (hd0,1), use what it comes back with in the next line

root (hd0,1)

setup (hd0)

quit

And reboot and if all went well you will have a boot menu.