I have two harddrives - one OpenSuse 11.4, the other Windows XP which grub was booting into either choice at startup. After upgrading XP to 7, only Windows 7 boots now - no grub. I've tried switching the harddrive order in BIOS - no help. Can you help me here?
Thanks!

Windows will overwrite other bootloaders.

Try reinstalling Grub. Google "reinstall grub" and you will find no end of links.

That is standard for a windows installation. It overwrote your master boot record. I would guess that you had the xp (now windows 7) drive set to first boot priority and Opensuse with the Grub bootloader on the second drive with a part of Grub in the MBR of the first drive. You just need to use the Opensuse CD to reinstall Grub. Boot from it and run this command in a terminal as root: fdisk -l(Lower case Letter L in the command) and post it here. If you want more detailed information, you can got to the site below, download and run the bootinfoscript and post the results.txt file here. This should be a pretty simple fix but without some detail on partitions it would be guesswork.

http://sourceforge.net/projects/bootinfoscript/

Read the instructions in the link in the Description box.