Yes you can, but you have to wait until someone releases more DX10 cards. Currently there's only one card being able to work with DX10 and it's not cheap.
I wouldn't be suprised that in the end Microsoft drops DX10 and reverts back to DX9 in some way (which they already taken steps towards by making Vista dual for DX9 & DX10), since there hardly seems to be any enthusiasm with hardware developers to even support DX10.
Having one card only for it even at the point of Vista's release isn't good at all.
Also buyers are holding off, since one card isn't much to compare and choose from. Buy 8800 for lot's of money now and see another Dx10 released in a months or so that is much cheaper and much better. If that will even be the case, since many game devopers and even major studios aren't planning on supporting DX10 for a while either.
I would seriously wait a while before investing anything at all into DX10, you may end up wasting a lot of money on some gadget. I'm still wondering why TGC is even running so much ahead of the market, they may be running into a huge disaster in the end, having spent a lot of time, energy and resources on something that may in the end turn out to be one huge hype and a lot of hot air. Wouldn't be the first time that happens when it comes to something Microsoft tried to push.....