What piece of computer hardware allows you to run multiple things at once?

[disturbed13]

all of this is great information

but i also have a diagnosis from what ive read

your PC is 2 yrs old (or close to it)
it doesnt matter what you do the registry gets full of crap
you can run some cleaners and such
but the changes dont hold a candle to what a fresh install can accomplish

so here is my suggestion:
google for a program called produkey
run it and save all of the product keys that it will show you in a simple text document
avoid using Microsoft Word
try notepad or wordpad
then save all of these keys on a USB thumb drive

then you should get all of your data that you want to save and copy it over to an external hard drive

then do a fresh install of your OS and copy all of your data back over

 

[MMM]

Do as what ja6on stated....defrag your hard drive as this will improve PC performance...
your registry files should be ok as nortons 360 usually does a good job of maintaining them.
If you are playing a high end video game and trying to multitask with other programs is not a good choice and definitely will slow down the best computers at times.

 

[setishock]

Oh good grief. This is so simple. When you open more than one resource intensive program and they use the same resources the os provides, the os will not duplicate the resource. You have several programs wanting to use the same resources and they have to wait their turn to get access.
This can be proven by opening one program and check the resources monitor. Open another. Check again. Open another. Check again. Keep going till you see the lag start. Back off one and that's your limit.
Having realtime anti-virus and anti-malware enabled will chew up resources like they are going out of style. Norton is as bad as AOL's software. It hooks in to your system in so many places you can kiss off any real performance. If you have those dump them and reinstall windows.
If not then a good place to start is in the services. But that's not a place for a rookie to go. You disable the wrong one and you're reinstalling windows.
With 4 gigs and assuming a 32bit cpu, might be time to upgrade to a 64bit system. And no you can't just swap out the cpu. The board has to support 64bit architecture.
Ball's in your court. How far you want to go depends on how much you want to spend...