Problem in booting after resizing partition

I have RedHat Linux and Win XP on my machine and was using GRUB to boot either of them. It was working fine with menu to choose the OS to load. I wanted to move some extra space from Linux partition to windows. So I used Partition Magic to free some space on Linux partition and merged it with Windows partition.

Now when I boot, I am taken to the GRUB command prompt. I tried to boot using Linux Intallation CD and also Win XP installation CD, but I always get to that grub command prompt. I don’t know what to do from there. Any pointers will be helpful.

Thanks.