Can i upgrade my computer still?

I've had this Hp pavillion a475c computer for 3 almost 4 years now and it can run guildwars on low graphic settings. Sometimes while playing guild wars, the video card makes alot of noise sometimes. And alot of times it lags. I'm not really good with computers so I'm gonna ask a few questions.

Can i still buy parts and upgrade this computer? If yes, which parts would be the best?

Is it worth it to upgrade this computer? Or build another one or buy buy a prebuilt one?

P.S: I'm on a tight budget. I can only spend about up to $500.00

moriz guide features a monster pc for 500$, you can't get better for that money.

If you have a little bit of technical savvy and computer repair know-how then get the compenents in Moriz's guide (sticky at the top of this thread).... great bang for the buck there.

That pc you have is too outdated to be economically prudent to upgrade now.... just go all new and you are better off by far.

You can still buy parts for that computer, but new parts would be relatively expensive. The only things worth upgrading (imho) would be increasing the RAM and getting a better video card. Overall, the price of DDR is not too different from what it's been (it's more expensive than DDR2 tho.) and you'd need a better AGP video card. Personally, I would check flea markets and/or local buy/sell papers and/or website for good deals on RAM and Video cards.

This depends upon what you call an "upgrade". I would say, given the specs of the a475c, that your most cost effective thing is to do a major upgrade to the computer.
If you are happy with the case of the HP, you should be able to fit a standard mATX motherboard in it.
So, you'd want a new (mATX) motherboard with appropriate cpu and 2 gigs of appropriate RAM (probably DDR2). A new PCIe video card and probably a new (larger) power supply.
The rest of the stuff - the optical drive, hard drive, floppy, etc., can be carried over from the old system.