Use the Applicatin Event Viewer (it's in administrative tools in the control panel) to discover why explorer.exe crashes.
One thing I would recommend is to use Safe Mode (hitting F8 while the white bars are at the bottom of the screen) to see if Explorer.exe crashes. If it does crash while in safe mode then find a hardware diagnostic program (available @ download.com) to test the processor and ram. If it doesn't fail then reboot the machine normally, and when you are at the desktop click the start menu and then the "Run" selection.
Type "msconfig" without the quotes and hit enter. You will see a startup tab. Manually remove the check mark in one of the boxes and reboot. Keep doing this until the problem is gone. Whatever the last check box removed was is the cause of the problem, and you can uninstall the app. It is normal to have some applications cause this issue.
When you're finished put all the check marks back accept the problem causer.