If you don't already have a 64-bit operating system, upgrade to Win7 Home (or Professional if you want XP Mode).
If you're running a 64-bit OS already, whatever you have will be fine.

6gb of ram will be enough, but 8gb is preferable.

The 9800 card will be fine, you'll want to run 1x AA and disable shadows in wow; probably minimum graphics on the slaves, and only view distance/spell effects up on the main.

A quad core CPU will be a lot stronger for boxing then your processor.

I'd look into a low end SSD drive.
Something to put your wow folder onto but not your operating system.
It's not essential, but its a huge performance boost.




If you can at all afford it, an i7 system is far superior for boxing.

I hate to recommend a quad core system to anyone.

The i7 means a new motherboard (x58 chipset is good) and ddr3 ram.

All the other components from the other system can work in this one.

But an i7 will definitely cost more.