Sundialvcs...thank you. You must be referring in part to my recent thread.
Mine is now resolved. When I reformatted windows GRUB dissapeared because, as you say, the mbr was over-written. I also had a reverse variation of the problem. Because so much of my hardware changed since the original install of Linux, I reinstalled my SuSE 8.2.
What happened then gave me some panic becasue GRUB could only see the Linux and I thought maybe I had reformatted my Windows XP NTFS partition into a Linux partition.
That was not the case. What actually happened was that the GRUB menu.lst file was missing the Windows XP entry, so a slight edit of the menu.lst in a text editor, adding Windows to the list, solved it. Someone should write a GRUB editing program for newbies like us and a lot of anxieties would disappear.
Here is my original thread for my problem, for reference if anyone needs it. This topic should probably be pinned, since I do see so many GRUB woes threads.
Thank you all for the help. This forum is great help for folks like me.