That doesn't sound right! windows7 is actually lighter on system resources than windows XP (as long as you turn off all the fancy visual effects)
Try the following, click on the start button, then right click on where it says computer and select properties, click on the link to advanced system settings in the left hand pane. once the system settings dialogue has come up click on the settings button under performance and then put a tick in adjust for best performance and click ok.
It will take a few seconds, and after that all the fancy effects will be turned off and things should speed up.
If they don't get your son in law back round and make sure that he did install all the correct device drivers for the hardware in your computer.