As Acanthus said, and I've been saying it. Any so called DX10 game coming out in 2007 is one where they throw in a few DX10 effects but nothing that big. Anyone remember the really early DX9 games? They were barely any better visually than DX8 games because they were basically DX8 with a few extra DX9 features enabled. There's nothing to suggest this cycle will be any different regardless of the wishful thinking of anyone. Ronin, who works for a games developer, even confirms that DX10 is not complete. Different sources have stated that at the earliest we won't see Vista (hence DX10) until the end of the year or probably not at all this year.
That means that Vista will have a very small installed user base this year and that the earliest someone can develope DX10 games with the final DX10 API's are late 2006. Again, we'll go by the 3 year development cycle that most state they need to make a decent game (stated by both console and PC game developers). That means 2009 would be the release date, or at best 2008, of any games that really make use of DX10. This pretty much follows the path of DX9 which was released late 2002 if memory serves me correct. It wasn't until 2005 that we really saw games take advantage of the extra features in DX9. Not to say that some games didn't make use of a feature or two of DX9 before that, just nothing that was a jump up in quality (visual quality at least, you can have a pretty game that still sucks rocks).
Malak, with all due respect, what game are you waiting on? What is so secretive about this awesome game that you can't mention it's name? Will the developers decide not to further it's development if you mention it's name? What? Curious minds want to know. Or are you afraid we'll throw evidence to show it's either 1) Very early in development and won't be out for a while or 2) Halfway finished meaning it'll mostly be DX9 with a few DX10 features thrown in. So far the only games that are even hinted at using DX10 features are Halo2 and Crysis. Is there a 3rd mysterious game we don't really know about yet?
I stick to my original opinion. Buy what you need when you need it. If your upgrade cycle happens to be now, then by all means, choose either the 7900GTX or the X1900. Both have their positives and negatives. If your upgrade cycle coincides with the release of the first DX10 cards, then get it then. But I wouldn't wait on upgrading specifically for DX10 features at this time. I still say that late 2007 is when one should start looking towards DX10 compliant cards.
Halo and Halo2 didn't impress me at all. If you want real Bungie games, check out Marathon Infinity and Myth. Now those were some games...to this day, Marathon Infinity had some of the most memorable multi-player gaming I have ever experienced. Marathon was open sourced before Bungie was bought by MS so while the graphics may suck, the multi-player fun is there in all it's glory. Funny with all the graphical advances over the years and one of the games I've ever had the most fun on is one that was in pseudo 3D much like Doom. Heck, it was out at the same time as Doom and a much much better game. Alas, it was never that popular in the PC world since it was mainly a Mac game.