Anyway, this is my suggestion for a semi-budget build
Foxconn A9DA-S $110.00
: AMD Phenom II X4 965 (3.4 ghz) $183.00
Gskill Ripjaws Series (4 gigs) $110.00
Phoenix Neo ~$80.00
Total Cost - $483.00
While not super top of the line, this would be a whole lot better than you have now.
So, Four gigs of ram would probably be fine to start with, if you want to go for 8, chances are you will eventually so you can if you want, when it comes to 3d, the processor is very important, whatever you do, don't skimp on it.
Motherboard - With all the happenings at Foxconn lately (non-technology related), I am semi-hesitant to recommend this to you, but it has nice reviews and is a good choice given your budget.
Processor - This processor should do just about everything you can throw at it.
Ram - Like I said above, you can get away with 4 No problem, and still have a bit of room to spare.
Case - I chose this mid case primarily because I know it does a good job cooling and is well laid out, also it has room for the new graphics cards with room to spare, which is rare in mid cases, feel free to go with a full tower though if you think you have room, also, newegg is currently sold out, but you can get this case allot cheaper else-ware. Also, if you want a full, the Antec 1200 series is nice, if not very bright.
Also, I recommend windows 7 for sure!