For the next year or so all the games will have dx9 support (even Crysis). So your x1950xt will do just fine. If it did have dx10 support it would probably do poorly. Even the 8800's haven't been doing so well in "dx10" enabled games suffering from fps drops.
Well like the others have stated, Crysis supports both dx9 n dx10 so ur card could very well last you thru out the next year (but with an average eye candy for the later games that is released next year) there will not be a dx10 only game for sometime..
DX9 games will still come out for a few more years.
The demise of DX8 didn't happen unitl after DX10 was announced and Oblivion was released. Therefore, games will still support DX9 until around the time when Microsoft officially announces that DX11 will be released for Vista.