Well, it HAS to have an MBR if you can see partitions. The MBR tells the drive where the partitions are and how big etc. So if it boots, and if you can see your drives.. then the MBR exists. However, I think it's possible to have problems with your MBR, but still have it work. This may be the case with you.
 
Be careful though, any messing around you do with your MBR can erase everything on that hard drive. Make sure to back up.

first, messing with your mbr cannot delete everything on the harddisk(s). second, you can prolly fix this by booting your win2k cd, choosing repair, choosing which installation, and going to the recovery console where you type 'fixboot' and 'fixmbr', that could do the trick for ya. btw, find it unclear whether you can boot the system as a whole or not, and av does take some recources, especially if you scan the master boot record.

If all else fails, you can re-construct an MBR from a floppy disk. Using a Windows 95/98/Me boot disk, boot into a dos proompt and type in
 
fdisk /mbr
 
it will not give you any messages it will take a few seconds then return you to the dos prompt. Next step, start Windows 2000 setup then abort it as soon as it starts copying files. Remove those files off your hard drive, then edit boot.ini to trim it down to what you want it to look like, then restart! ;-)
good luck!

take Norton off of it man, i can't think of a more pathetic/memory-hog program.