Yes and No. It depends which files you are talking about deleting
Deleting things out of the temp folder could help. Also running anti-virus and anti-spam software to remove that sort of stuff can help.
You can get both for free with the Google Pack http://www.google.com/pack
Norton Security Scan
Spyware Doctor
If things do start running slow and you get alot of blue screens, then you will need to reinstall the OS and all the software. that is guarentted almost to make it run faster. it is the most time consuming of them all since you need to reinstall everything.





