major system slowdown

Trying to help my dad. I'm a former IT professional, though not on the tech side, my dad is basically computer illiterate. His machine is an HP Pavilion 512n with XP, 156MB RAM. Not even close to being new. About 2 years ago it started slowing down for no apparent reason. At the time McAfee was installed as well as AdAware and Spybot S&D. They showed no problems. Ran defrags and cleanups. Installed System Mechanic and it fixed a few things, but didn't help. Things continued to get worse, so about a year ago we did a complete reformat and restored to out-of-box condition. That helped, but only minimally. Online diagnostics sites say to get more RAM. 2 problems with that: 1)if the only thing wrong was RAM, then the slow-response issue should have been present straight out of the box and 2)financial resources are already stretched TIGHT. Recently the problem has gotten so bad that even a simple program like solitaire takes 30 seconds or more to deal the opening hand. Any help would be greatly appreciated, especially since about 6 months ago the same thing started happening to my laptop (also an HP but not nearly as old).

 

Vendors who sell undersized RAM-CPU comps for newbies should be considered as liers. Don't expect to run XP correctly, the swap file on your HD must be terrific and it slows down the system from day to day.

 

Defrag the HD (in safe mode) then cut down the autorun package to a minimum. Set up a fixed swapfile of about 4x the memory. Uninstall one of the anti-spyware programs.

 

My Dad lives about 2 hrs away, and I'm back home now, so it'll be about a month before I can do any more. Meanwhile, I'll see what these suggestions do for my laptop. Before coming home I did increase Dad's swapfile size. About every other visit, I run System Mechanic to try to keep his PC in as good a shape as I can.
Thanks for the tips. I'll post any changes/improvements as noticed.