In that case the problem may lie with your XP.
What you can do is to make a bootable Grub floppy for your Suse and restore XP's MBR.
To make a bootable Grub floppy just log in as root, pop a floppy into the drive and type
Thereafter you can either boot a Dos floppy (Dos 6 or above) with fdisk.exe inside and type
alternatively you can boot up the PC with a XP or Win2k installation CD, wait until it offers installation or repair, choose Recovery console to repair and get into command prompt. Just type
From this point onward XP should be booted by its own MBR and you can boot Suse by the floppy.
Any time you want Grub back into MBR just do the same thing of making a floppy except the destination should be /dev/hda instead of /dev/fd0.