Well any system lagging around is not good. Lets see if we can get the old girl back to her perky self.
1> Defrag This will make it quicker for the system to find files.
2> Edit the start up programs in msconfig. Here you can get in the soup real easy. Turn off by unchecking any program you don't need to start up when the Operating System loads. If you have any doubts, leave it on. Better than getting locked out of your system.
3> Run a good ad/spyware tool. AdAware and Spybot S&D for a good one, two punch on the nasties. See this thread for the links to where to get them>>>http://www.computerforums.org/showthread.php?t=12198
When you get them be sure to go thru them and set them up as to what you want them to do. Update them before you run them.
Well that should get some rise out of the old girl. But just so I'm sure it's a software problem how about posting back the specs on your system.