Basically,
You need to resize that XP partition (what filesystem are you using? NTFS or FAT32?). Then
you need to create an
extended partition using the whole space that you released.
After that you can use the linux distro's install procedure to create the linux partitions.
You'll need at least two a linux root "
/" and a swap partition. You distro should create
them for you, the swap should be around 1.5 to 2 times or system memory, but unless you'll
use some programs that use a lot of memory, or use the system on a multiuser enviroment, you
can probably just size it to 128 or 256 MB.
After creating the partitions just go with the default options untill you get into
Boot Loader
installation, there you should install the boot loader into the the root partition instead of on
the Master Boot Record(MBR). You can probably install it to a floppy it will be a lot easier to
begin with.
For the rest read:
Linux + NT Mini Howto!!
And the faq page suggested above!!