installing ubuntu thaqn xp

I have been using Linux for years but recently decided to completely eliminate xp with one exception, for playing DVD's. I had the computer set up with ubuntu and xp but then I reinstalled xp (Not thinking!)
Now grub doesn't load so I am unable to load ubuntu.
I have tried this
http://apcmag.com/how_to_dual_boot_linux_and_windows_xp_linux_installed_first.htm?page=5

Buyt whenever I get to the setup (hd0) step I get
Error 17: Cannot mount selected partition

I think this is because I use two hd's. One for xp and oner for ubuntu.

Does anyone know a workaround? thanks!
ingalls