More info please.
Open task manager, click processes tab, keep an eye on all under cpu, post a list of the top 4 names that are using the most cpu & how much for each when it starts to freeze.
Are you using.
internet explorer 7 or 8?
Name of anti virus scanners on your pc?
Name of spyware scanners on your pc?
Did you install anything before this started to happen?
Erk, July 2009