Ok let me try to be specific with an option, ok? A computer will slow if you don't have enough memory alloted for temporary files.

Click Start
Click Control Panel
Click System
Click Performance
Click Advanced see processor usage, memory usage, virtual memory ADJUST This.

Click CHANGE on virtual memory... and adjust the amount of memory UP so the computer has more to work from when accessing pages etc. The other adjustments can help too... but this is the best way I've found... the other procesor and memory usages I have to run the programs, rather than the cache, btw.

Good wishes!