Try Disk Cleanup first.....go to Start>Programs (or All Programs, if using XP Start Menu)>Accessories>System Tools>Disk Cleanup. Under the Disk Cleanup tab, scroll down to locate "Temporary Files" and if there is no checkmark in the checkbox beside it, click in the checkbox, then click on OK and then Yes in the "Are you sure?" dialogue box. Once Disk Cleanup has finished and exited, restart your computer and see if you can now install one of the applications that you were previously unable to install.