You can get a significant performance increase by upgrading the PSU and getting a good video card.
The Antec PSU recommended above is a good one - but you can get another good one for less - the Corsair Builder Series 500w for $40 AR
Newegg.com - CORSAIR Builder Series CX500 (CMPSU-500CX) 500W ATX12V v2.3 Active PFC Power Supply
For video cards you have a wide range to choose from. Note that you use programs like Maya that benefit from the CUDA feature of nVidia cards so I suggest sticking with them.
If you can afford $130 for a card, then I recommend the GTX 460 768MB card. It is a solid card that can be found at a discount right now because it is being replaced by the GTX 550 Ti, but the new card is slower. The 768MB version of the GTX 460 is only slightly slower than the 1GB version, but costs substantially less. See the slight performance difference in this article:
Nvidia GeForce GTX 460: The Fermi We Were Waiting For : GeForce GTX 460 At 1 GB And 768 MB
Note that on the THG Best Card for the Money article linked below, the GTX 460 1 GB is one of the cards recommended at the $200 price level. This card is almost as fast and as shown in the review above, and costs quite a bit less..
Best Graphics Cards For the Money: March 2011 : March Updates
For a specific card, I recommend the MSI Twin Frozr because of its effective but quiet heatsink/fan, factory overclock, and good price – only $130 after rebate.
Newegg.com - MSI N460GTX Twin Frozr II SOC GeForce GTX 460 (Fermi) 768MB 192-bit GDDR5 PCI Express 2.0 x16 HDCP Ready SLI Support Video Card
If you want to spend less on a video card, then take a look at the different video card upgrades recommended at different budget levels at this site:
Best Video Card Uogrades for Non-gaming Use
I was curious about the speed of your CPU so I looked up its performance - its not as slow as I expected - but of course not as fast as the newer cards. FYI the chart below shows the performance of your CPU compared to a current favorite - the Phenom X4 955.
Compare , AMD Phenom X4 9150e (Agena 4c)