Get Partition Magic 6.0, or maybe 8.0. I think 8.0. Anyway, it's not the latest one. Install that in MS Windows XP. Make a rescue disk set. Boot the computer with the rescue disk set. Or, you can just find a set of Powerquest Partition Magic rescue disks. Actually, you can just pull the file PQMAGIC off the CD, put it on a floppy. Boot with a DOS floppy, put the floppy in with PQMAGIC on it, and type PQMAGIC. Partition Magic will start. Make a primary partition for the linux root. Don't format it. Make an extended partition of the rest of the disk. Put in the extended partition: An NTFS partition for MS Windows XP and format it with Windows XP type NTFS.
While you are doing this stuff, I want you to apply the changes as you go. So, if you do one thing, apply that change before you go on. In the extended partition also make a "swap" partition for linux, but leave it unformatted. Swap should be about 1 GB. In the remainder of the extended partition make a partition for linux "/home". You don't have to specify mount points in partition magic.
Ok, when you get formatted, reboot with the Windows XP install CD. Install XP to the logical partition that you made an NTFS partition. When you get to that part of the install, you will see it. Go through the whole install, and install Windows XP new.
Then shut down.
Do a linux install. It should guess what you had in mind with your partitioning. Let linux install, but make sure it picked the small partition for swap, the medium partition for root, and the giganzo partition for /home. You can let it repartition, too. But make sure those partitions are correct. You want about 10 GB for root. That is the only primary partition.
After linux installs, you will get a boot menu when you boot up. Grub will have moved the Windows boot files to the logical NTFS partition. Grub aimed pointers with the function chainloader at these files. Now your primary partition is safe. Linux has taken over, but made a special place for Windows XP where it won't get out of hand, and try to run the show.
Make sure you do stuff in that order, how I told you. That will work.