high percentage of cpu usage, means programs which require ram are running.
Programs that you might have that use up a lot of ram.
Norton antivirus
Macafee antivirus
Solution, get rid of them and get a freeware such as Free AVG (it's free, just like the name says) which takes up less memory to run.
Other issues that could be causing this.
If you notice a lot of popups when you go to websites that normally don't have popups (like google.com for instance), then you have adware on your computer.
Solution,
Save all your data to disc or backup drive and then reinstall your OS to factory defaults, since there is no way I can possibly go through all the different adware removals that you could possibly do.
Also, try turning off any and all items running in the background that do not need to be running at this time. Use your process viewer for this action.
Last but not least, instead of having all of your ims open at the same time (yaho, aim, msn) get trillian, or someother chat program which can tap into all three, this way, you only have one program open for all of your chats.
Hope this helps