No keep your 7950GX2 until a)you can't play games that you like to play.
b)if that doesn't happen then whenever the dx10 game you want comes out then buy a dx10 card. otherwise you'll will have pretty much wasted money since your current card is more than capable right now. the method i suggested will ensure that you pay the smallest amount for dx10 rather than paying alot right now only to find out it was twice as cheap when a dx10 game you actually want to play.
Vista does not require a dx10 card to enable its features,any low range graphics card can do that...
DX10 will not be neccesary for a long time and will not be particularly beneficial for at least 6 months or so. You should wait until late summer or so at the earliest unless you have ungodly amounts of money laying around.
It's a bit like asking "I've got a car that does 150mph. But there's a new one that does 160mph. Should I sell my slow car and buy the new faster one? The new fast one also has cup holders for holding 1-litre bottles, which hardly anybody uses now, but they will be in the next 2-3 years."
IMHO, the nVidia marketing machine has done a damned impressive job of hyping the 8800 series. I saw the GTX in action the other day... Ok, so it looks good... but it's not THAT good... You can build a whole system for the same price as one card!
I never said anything about the new 8800GTS 340mb performance, i said the advice you gave was terrible cause why would he spend $300 on a new graphics card when his current one will suffice. if he was playing oblivion and said he was getting lagging fps then and he needed a better card then yeah get it.
But he didn't say that, he asked would be worth it to go to DX10, all of which there is no point to buy a card simple because it is a DX10 card right now cause obviously the operating system isn't even officially out yet, and also no games fully developed around dx10 are even out, let alone a game that he would like to play.
Now if he said he needed more performance right now then yes any 8800 series card would be the best to get right now as its the best performing DX9 card on the market.
The best and most logical thing to do would be, since he already has a very sufficient graphics card and didn't complain of needing more performance, to wait until the DX10 game he wants to play comes out, at that point he will have waited till the latest possible date until he would ever use DX10, this would ensure that he saves the most money. Instead of spending money now, when he wouldn't even need the DX10 feature, when he could get it for possible half the price later. On top of all of that by the time the DX10 game comes out that he wants to even play there will be ATi's new card, and nVidia's 8900 series, all of which means lower prices and more performance.
So yeah thats a better idea. No need to waste money now. Now if had a under-performing 7800GT or something else like that then it would be very obvious that if he had the money to get an 8800 series as they offer the best performance right now.
Most people who buy graphics cards for upgrading the PC tend to be people who know SOMETHING about them... You don't often see some noob who knows nothing buying eBay cards. People like that tend to think AMOUNT OF RAM = QUALITY OF CARD and end up with some shitty X1300 from Tiger. Ugh.
This is even true for me, when I built my first computer I bought the cheapest 256 mB GPU off of Tiger. (it was a 5200 )