For an attempt at actual useful tips:
Run an anti-virus and anti-spyware program to ensure that there isn't anything rouge that's absorbing CPU cycles

Increase the minimum and maximum settings for virtual memory. This should help with the "Virtual Memory Minimum too Low" messages you sometimes get on Windows XP

Open the task manager and sort your running processes by ram usage. If there are any suspicious processes, google them to see what they are. If there are ones that are using lots of memory that you aren't using at the moment, quit using them! If you are using them, see if there's a way to make them use less memory. Browers are notorious for this, the solution is to a)use less tabs, b)close and reopen the browser to reallocate memory lost to memory leaks and c)switch to google chrome!

And finally, what I've been suggesting to my mother for about 4 years, BUY A NEW COMPUTER!