If you couldn't access your actual C drive, then it is probably formatted as NTFS (win98 cannot understand NTFS, but it can FAT32, which is probably the drive that you can see). Boot using the WinXP CD, go into recovery console (you may be asked the administrator password), then you can move your .bak file back, and you should be able to boot fine. If you can't get it working that way, then again boot using the WinXP CD, and choose the repair option...it'll basically upgrade WinXP over top of itself, and should replace those files with good ones (you will need to re-install any updates such as service packs, but your software and data should stay intact).