I have heard of a program for the PC (XP) that allows you to try out
installing other programs safely (? in a special guaranteened area of
the hard drive), so you can trial them for as long as you want and
then completely remove all traces of them if they don't perfrom to
expectation.   What is this program(s)?

The safest way would be to use vmware. Vmware allows you to install a
"virtual machine" inside of your existing operating system. In that
virtual machine, you can install a new copy of Windows (or even
Linux). Anything that happens in that virtual machine is kept
completely isolated from your original operating system. Vmware isn't
cheap, however. Check out
http://www.vmware.com/products/desktop/ws_features.html

http://www.soft32.com/download_102.html Total Uninstall should help(free)