Within the last 5 days I readded SuSE 9.1 and XP to dual boot on my machine. It dual boots through grub fine and SuSE did it all for me. I didn't even have to mess with the boot loader. Only problem I had was it couldn't create a swap file (some googling revealed this was due to the NTFS partition on hda1 (c)). So I don't have a swap file but SuSE was kind enough to tell me how to do it later then said "I'll finish the installation now, thank you."
I ran into similar problems though when I tried to set up my machine for XP on one disc and SuSE on the other. What I figured out was I basically had to use yast to tell grub where the boot info for XP was. Unfortunately, a childs finger loved hitting the power switch and crashed it all.
While reinstalling, I discovered it was much easier to install XP first one one drive only. Then Install SuSE on the second and tell it whre to put all those partitions and files. It's worked quite dreamy since. As soon as I unlazy myself, I'll put a swap partition back in.