What mixes me up is the different names for the processors. Athlon, Duron, Sempron, Pentium, Celeron, etc. I think a Pentium4 is better than a Celeron but why? The AMDs I have no idea which is better, I think Athlon but I don't know. Is it the cache size or is one chip just better quality? I would like to be able to play newer games like Doom3, Half Life2, etc. Should I upgrade what I have or get a totally new computer? I have a HP Pavilion 8650c with 533MHz Celeron and 512MB RAM. I'm still running Windows 98SE.

hey, sorry for replying so late, but you can tell which one is faster by the GHz. I would say minimum you should go with is probably 2 ghz. i have a 2.2 amd athlon xp and 512 ddr ram and all games work fine.

What mixes me up is the different names for the processors. Athlon, Duron, Sempron, Pentium, Celeron, etc. I think a Pentium4 is better than a Celeron but why? The AMDs I have no idea which is better, I think Athlon but I don't know. Is it the cache size or is one chip just better quality? I would like to be able to play newer games like Doom3, Half Life2, etc. Should I upgrade what I have or get a totally new computer? I have a HP Pavilion 8650c with 533MHz Celeron and 512MB RAM. I'm still running Windows 98SE.

You may need to replace a few parts on your old comp to get it up to speed. If you get a new CPU, you will probally have to get a new motherboard. For instance, going from an Intel to an AMD chip, or just getting a faster processor. Older motherboards can't handle most of the faster processors out today. To add to this, you need to make sure the motherboard supports the socket type of the cpu you are buying. This is the number of pins on the cpu, and their configuration. To add to this, lol, you may need to upgrade your power supply in your case if you buy a Pentium 4 or an Athalon. The newer motherboards/cpus require another 12v conneciton to the power supply.
You may be able to reuse your memory. I know memory (RAM) is backwards compatable, as long as the pin setup is the same, but I am unsure if a motherboard which is supposed to have a certain type of RAM can have a slower one installed.
As far as other stuff goes, you may need a graphics card with 3D support, or a motherboard with good onboard video.
Taking all of the above into consideration, you should check out www.newegg.com for your parts. They have awesome prices, and have pretty quick processing and shipping times too.
Is sounds like you may need to upgrade a lot of stuff on that comp to make it work. Heres a few prices that may help you size up what you want to do:
A case with power supply (almost the same price as just buying the power supply) is like $30 after shipping
A new cpu and mobo combo: Celeron D cpus are $50 to $100, Pentium 4's start around $100 depending on what you want. Motherboards for both are anywhere from $40 to $140 lol.
RAM: 512 mb is around $40 to $50 shipped for budget......
Graphics Cars: What ever money you have left

To be honest with you, its hard to just reccomend somthing. I could tell you what I have for a box, or tell you what Ive built for people, but the choice really relies heavily on what parts you want to keep, and what your budget is. You may want to buy WIndows XP as well. Home edition should be fine for you. So theres another $100. If you want to build your own box, you could build a full one for like $400 or so. But in saying that, Best Buy, Wally World, and Circuit City have deals sometimes for a full computer setup for around $400 or $500.......

I tend to agree with freek on upgrades. Any system over 2 years of age can not be upgraded economicially. What you will wind up is with a 2 year old case with all new hardware inside. Now this might be fine and dandy for geeks like me (6 YRO case and 1-2 YRO hardware. Don't get me started on telling you about my hardware!) and freek. If you want to, welcome to the REAL world of high performance computers.

There are alot of paralells between PC manufacturers and car companies on how they design and build their products. Especially in the performance regime.
Their mantra is profit/loss ratios, rarely will you see a genuine high performance product hit the market that you can afford without your wallet crying.

If you are willing to join us in the deep end, welcome aboard! Just keep a tight screw count and wear an anti-static wrist strap to keep from zapping your pride and joy. It's one thing to mis-wire the front buttons and lights on a case, but it's another to lose a screw, only to realize too late that it's wedged between your 200 buck mainboard and the case, grounding it out and frying the hardware.

LOL. True, true. Lost screws can wreak havoc on a box if they are in the right (wrong for you) spot ;).