Would like some advice for my Upgrade on a budget

Hey all!

Well, after many years of my computer running quite faithfully, the time has come for me to upgrade. I am pretty out of the loop when it comes to computer hardware these days, so I was hoping you folks could help me out with providing feedback on the upgrade I am planning.

Budget...
$600 for Motherboard + RAM + Processor + Video Card

My current computer...

• AMD Athlon XP 2500+ Barton
• MSI K7N2 Motherboard
• 1 gig of random DDR ram, don't even know the brand
• Radeon x850 video card (AGP)

As you can see, my current computer is pretty damn old. It is able to run a game like WoW "ok" but even that lags out in highly populated areas. It can't run Age of Conan at all, even with everything cranked to minimum. It can just barely run Warhammer Online.

My planned upgrade...

• ($170) Intel Core 2 Duo E8400 Wolfdale 3.0GHz 6MB L2 Cache LGA 775 65W Dual-Core Processor
• ($140) ASRock P45R2000-WiFi LGA 775 Intel P45 ATX Intel Motherboard
• ($78) A-DATA 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory
• ($210) SAPPHIRE 100242-1GL Radeon HD 4850 1GB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card

Total: $598

What I want to do with it...
I am a big MMO guy, so I want to be able to play games like Warhammer Online or Age of Conan and not get lagged all to hell when a fight with a dozen players breaks out. I don't need to have every last graphics setting cranked to full, but I also don't want the game to look like crap, just so it wont lag.

So what I would really like to know is...

• Is this upgrade I have planned a nice bang for the buck?
• Will it be able to run games like Warhammer Online, Age of Conan, and World of Warcraft with ease?
• Are the combination of parts I have chosen likely to work well together? (I'm not sure if certain brands of video cards favor certain brands of motherboards, etc.)
• I was thinking about getting a single Radeon 4850 now, and then sometime down the road, getting a second one and do a crossfire setup. Think that is a good plan?

I really appreciate any help you all can provide. Thanks much!

All good choices. I believe A-Data is another RAM manufacturer that generally adheres to the 1.8V standard. I use Mushkin in my rig because it does too.
As Nytmare said though, be sure your PSU is up to the task. Corsair is an excellent brand. Antec, OCZ, PC Power & Cooling, and Seasonic are also among the good ones. 500W-600W should be sufficient, and allow some headroom.