Here's my specs:
Built 2 years ago...have been using the same PSU since its creation
4 gigs of RAM
EVGA Nvidia GeForce 9800 Gx2
AMD Dual Core Processor @ 3.0 Ghz (I think the series name is Windsor)
ASUS M2N32-SLIDeluxe Motherboard
X3 Ultra PSU @ 1000-Watt PSU

I think that's all the relevant information you should need regarding that.

Here's my problem. I can barely run WoW right now...let alone 5 box. I have never been able to 5 box efficiently however I would really like to see if it's possibly my power supply, or maybe my video card is a little shot. I have already reformatted a couple times, as well as made sure all my drivers are in order.

I really think it's my power supply but I really have no way of checking, at least not any time soon.

On to my questions...:
1. With this computer setup, should I be able to 5-box, if even not that effectively(i.e. 30 fps on main screen, 10 fps on the slaves)?
2. What is a good way to check if it's my power supply?

I know I'm making quite a bit a wall of text, but I'm also looking to build a new computer here in the future capable of multiboxing. I've come up with a shopping list, but honestly, I'd rather see someone who is more experienced at multiboxing possibly put together a list. My budget will be around 800-1200 dollars. I'd really like to go quad core with 12-16 gigs of RAM.

Thank you for any answers/support