Speed up slow computers

Thank you for veiwing my post
I have two computers which seem to be running slower and slower while browsing the internet.
Both computers ate networked thru a cable modem, I have called the ISP and they "pinged" my system and all is running at posted speed, I have also reset (by unplugging and replunning in the modem) my cable modem.
My main computer is a Compaq Anthlon 2.16GHz 512 mg ram, 120gb HD and the other is an eMachine Celeron 500MHz upgraded to 256mb ram and 120gb (Maxtor) HD, both are running WinXP Service Pack2.
I don'y do alot of heavy downloading, mostly browsing (Google, Yahoo, eBay ect...)and I try to do maintenence monthly DiskClean, Defrag, Antivirus (Norton and MicroTrend), Spybot, and AdAware.
I seems as if pages take forever to load (5-10 seconds) can you help.
I'm certain my startup tray is way too full, but I'm not sure what to keep and what to delete (although I don't think that's the problem).
Also I've been told to delete TEMP files (Not sure how to do this)?
Finally, when looking in Windows Explorer, I have duplicate users of the three users I have for my computers (How do I know which to keep and which to delete?).
Since I am a novice I'm certain the simplest answer will be the best please help.

 

there's a program called ccleaner on this site which might help, it will remove ALL temp items on your PC or tweaknow reg cleaner is good too for registry clean up ... also might try using Firefox instead of IE ... if you are using the built in defragger you might try O & O Defrag or Diskeeper ... spybot has a handy tool to reduce the amount of start up apps, some of them do take a lot of resources depending on what they are

I've noticed that for some reason or other my internet slows down the longer I have a system running ... so sometimes the best thing is just to do a full reinstall of your system and start fresh