Google for the terms: NT Grub Duel Boot "How to" for a number of how-to's on the web on how to use the XP's loader (it uses the same program NTLDR.exe) as Windows NT does.
The process takes a bit of work but isn't to complicated. It involves writing either the lilo or grub boot loader to the Linux root partition instead of the mbr, using the 'dd' command to copy the bootstrap code to a file on floppy, copying the file to C:\, and adding an entry for it in the 'C:\BOOT.INI' file.
This method doesn't change the MBR at all, so you will be able to boot up Windows XP without any problems.
Here is on such link:
http://www.geocities.com/epark/linux...w2k-HOWTO.html
You should be able to ignore the part about the 1024 cylinder limit unless you have very old computer.
---
P.S. In my own experience, I've never had a problem with installing the boot loader to the MBR on a laptop (On 5 laptop models, 3 of them with XP ), but I've had a problem once on a desktop.