I have XP pro, Mandrake 10.1, SuSE 9.1 and am gettin ready to install FreeBSD (new to that one) , so yes, it is possible. If you don't care for linux, you can fix it by these steps
1. insert XP CD
2. Reboot computer, boot from CD
3. Choose to recover windows from recovery console
4. at the recovery console, type fixmbr
5. Follow directions
this will fix the MBR and allow you boot to windows XP without the use of a bootloader. then you can keep the extra HDD and do what you will with it. This works for one drive/multiple OS's or two drives/multiple OS's
Some sites I found useful
www.linuxselfhelp.com
www.linuxhelp.net
www.control-escape.com
Also, What distro are you running with?
If you want some choices, check out these two sites
www.linuxiso.org - not always up to date, but still got some goodies
www.distrowatch.com - pretty up to date, keeps good track, lots of distros