I have a Laptop about 5years old with a Pentium 4.CPU 1.00 GB Ram 40Gb HD Windows XP Kaspersky Virus Checker I have recently had Belkin 54Bps Wireless Adaptor fitted. I have found that it is very very slow, when you go to close down file it Freezes. Some programs will not open all I get is the hour Glass. I have tried to Defrag but that locks up I have ran CCleaner, Regseeker nothing seem to cure the problem.
My daughter had the same problem after installing a wireless connection on her laptop the problem turned out to be Microsoft Windows auto update. Because she only connected to the internet occasionally the computer was using all its resources to cope with the updates. I have turned auto up date off and this has cured the problem now she does manual updates when she decides to. May not be your problem but just a thought.