What should I upgrade?

[Graves]

With cataclysm coming up soon, I've seriously started to wonder what I should upgrade on my computer. I have a general idea, yet I don't know the specifics.
My current specs are:
-Intel Pentium 4 CPU 3.00 GHz (I know this is REALLY old. I just don't know exactly what to upgrade this to)
-2.5GB of ram. (It isn't DDR3, if that makes a difference.)
-NVIDIA GeForce 8400 GS graphics card
-22 inch Samsung monitor

As you can tell I'm not TOO too computer savvy. Would a quad-core/tri-core make a phenomenal game play difference?
I run at anywhere from mid 20-30 frames regularly, and 10-15 frames in Dalaran.
As for my budget, Christmas is coming up soon, so I may be able to get myself some upgrades, along with Cataclysm.
Any thoughts?

[Kärmä]

I've heard WoW is a CPU hog so maybe a new CPU?

[sciarc]

With a system that outdated you likely aren't going to be able to upgrade just a component or two - you will probably have to replace everything, other than the monitor (and maybe hard drive and power supply).

I'd suggest doing a little research on sites like tomshardware or anandtech to get a feel for what's currently on the market. If you're on a tight budget you'll probably be looking at an AMD CPU, such as an Athlon II X2 or X3. These will require a new motherboard and probably RAM as well, but will give you a huge performance upgrade for not too much money.

As for video cards, you can probably get a huge performance upgrade for somewhere in the $50-100 range.

Shop online for combo deals at places like Newegg.com, you can save quite a bit buying a CPU/motherboard/RAM combo.

[Furbolg]

You're gonna need a new motherboard, CPU, RAM, graphics card, and probably power supply as well. Basically your computer doesn't have parts that are worth keeping, except maybe your hard drives if you want to keep your data.

[kallette]

Basically your computer doesn't have parts that are worth keeping, except maybe your hard drives if you want to keep your data.

This, imo, except I would recommend you replace your hard disk as well unless it's newer than the rest of the machine. The longer you hang on to a hard disk the more likely it is to fail. Disks are getting faster and faster, and it has a significant impact on the general performance of the machine [though not so much in games]. And you would want to format your old disk anyway if you're gutting the machine. Oh and they're ridiculously cheap now so you might as well.