It would sure help if we knew the operating system of the infected machine.
Here's McAfee's write up about the virus that should help:
Here is a "stand alone" tool from McAfee that can be used to remove Bagel. It can be downloaded on a clean computer, placed on a floppy disk, then transfered to the infected machine.
McAfee Stinger Tool- Removes Klez/Bugbear
After placing the tool on the desktop of the infected computer, restart the machine to "Safe Mode". Double click on the "Stinger" tool and run it repeatedly until it comes up negative.
If the infected Explorer.exe actually resides in the "C\Windows" folder, and IF the Stinger tool can't repair it, then the Explorer.exe will probably need to be restored while in a command line of some type. When "Explorer.exe" is deleted, Windows probably won't load. Depending on the operating system, it could be done by extracting the file from the Windows CD, but because there are so many infected files, it may be necessary to reinstall Windows.
Hope this helps.