I may be misunderstanding you - but I think you'll have the best luck if your windows partition is not being used as your Linux partition as well (I don't even think that's possible with XP or 2000, but only with the FAT16/32 partitions used by Windows 95/98/ME). Linux can read the XP file format (NTFS), but writing to it is not considered a good idea.
If you were going to use Fedora, I'd suggest resizing the Windows partition ahead of time using BootIt-NG or Partition Magic. From what tomf87 is saying, Suse will even handle that chore for you - probably with a tool called parted (you don't really have to worry about remembering that!). But the end result is that a part of your disk (a partition) will have the Windows installation, and the rest of the disk - divided into one or more additional partitions - will be used for the Linux installation.
Make sure Suse says it will resize NTFS partitions BEFORE you start. If there's any question,
you can use a program called BootIt-NG (free trial) to resize the NTFS partition without destroying your data.
Both Suse and Fedora use a program called grub that will basically control the computer's bootup by installing itself into your disk's boot partition - this type of program is called a "boot loader". When you turn on or reboot your computer, you'll see a menu that will basically say "boot into Linux" and "boot into Windows", allowing you to choose one or the other.