I would suggest, don't upgrade the whole rig for the time being.
Just use a little money from your budget and get the AMD FirePro or Nvidia Quadro Card.
Use it on that rig itself. You will be able to use it pretty well for those applications for another year with one of these cards. And it'll make the rig a lot more fast. Get used to those cards first see how they help you out and if you feel you need to go higher with the specs we could suggest a nice not too expensive upgrade later.
Later on. Go for a good system with a 64Bit OS and a minimum or 8 GB DDR3 RAM.
Here is a list of the cards that will be compatible with your present mobo and available on newegg.http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100008333%20600044676&IsNodeId=1&bop=And&Order=PRICE&PageSize=20