Hey,
you pretty much have the same question I had not too long ago..
If you're limited to $150 for a VGA, you're better off using $50 (or more)of your mainboard limit and putting it in the VGA limit.
In my "Harnessing 3DS Max 8" book, it says 3DSMax relies mostly on Ram for the stack, so I'd reccomend at least 2GB DDR2, Since I have 1GB and its slower than my friends computer, and painfully slower when it comes to high stack and high poly scenes.
Personally, I'd get an 64-bit processor with 4GB Ram to run 3DS Max 9 x64, but I'm not ready to buy the upgrades or let alone buy an upgrade of the software.
For a motherboard, just go into Newegg, and perform an advanced category search, putting it everything you need. Also, check out tom's guide to motherboard selection.
For the VGA, I'm not expert, since I had a limited budget to $300 for a new mainboard and a VGA ($200 for the VGA, $100 for the mainboard), I chose a X1900GT since I use 3DS Max for modding the Source engine, and I regularly test my progress in game.
But for you however, you might want to consider a 7900GT (
http://www.newegg.com/Product/Product.asp?Item=N82E16814127218 ) since this one is $235 after the rebate.
If you do not game, consider the Quadro of FireGL cards, but I never had any of those so I'm no expert on it.
Hope this helps,
DarkAlien