Dual Boot

I have a PC running Win98 SE which carries out some very processor intensive functions which can interfere with day to day business and vice versa.

I would like to be able to boot the PC into two different configurations.
1) A ‘clean’ config that loads only those drives and software necessary for one of the PCs functions
and
2) A ‘general’ config that loads up the day to day packages i.e office etc.

I would like to do this without resorting to using any software package but don’t know how.

Any ideas?