For programs, you should go to "Start>Settings>Control Panel>Add/Remove Programs"
Another good thing to do would be to do a Disk Cleanup. "Start>Programs>Accessories>System Tools>Disk Cleanup"
After that do a defragmentation. "Start>Programs>Accessories>System Tools>Disk Defragmentation" (You can't open any programs or have any along your program bar at the bottom of the screen while doing this. And it may take a long while)

I do this every week, but I'd recommend once a month.