It may be that you need to add more RAM to your system.Do you know how much you have ? If not follow this Click start , point to programs , accessories , system tools , click on system information , on the right of that window will be the percentage of system resources , what does it say ?
You could also delete temporary internet files to free up valuable resources , to do this click internet explorer , then tools from the taskbar at the top , internet options , general tab , click 'delete files' button under the Temporary Internet Files section.You could also do a defrag .To do this go to start , programs , accessories , system tools , defrag.
You can also download a program that will get rid of clutter on your system for you , there are many out there one of which you can get from here called Clean up users3.ev1.net/~stevengould/cleanup/download.html
Let us know how you get on.