If you can get to the DOS prompt (try pressing F8 just before windows screen boots up) and select DOS prompt only, you might be able to get the system going by typing 'sfc' at the command prompt.
For this to work properly, you need the CAB files (original Win 98 CDROM files) located in the PC somewhere. This is a windows command that replaces damaged system files. It might just work, you never know. For more info search google for sfc.