Questions on system specs for DX10 and upgrades

Will Vista be worth it when AoC goes to DX10 or rather would it be worth revamping some stuff to use DX10?

my setup is as follows:

Intel Quad core 2.4 Ghz processor
MSI Aseus motherboard
4 gig ram
150gig hardrive
"1" 8800 GTS XFX

second question is if i do go for the DX10 spec im already able to use it but would it be smart to grab another 8800 GTX XFX card to SLI dual them ? or would it be better to buy a 9800 series card?
any suggestions would be welcome!

personally i wouldnt spend an extra dime (outside of building a system that i already needed) for that type of upgrade (dx9 to 10) but maby after seeing it i will change my mind.

granted i built my system to specifically run dx10 so maby i'm not one to talk

yea thats what i did I told myself "Direct X 10 will be good i gotta make something" but im still running XP so now whe it comes out i gotta see if its worth dropping a 2nd graphic card or a higher end one or going to vista "which id have to anyways obviously" but ya know

I have heard XP does not utilize the quad core well, is that true?

well with the setup i have right now its running fine i havent had an issue at all with it another complication though is i was thinking about trying out that 3 core AMD processor..."since AMD is known to be better forgaming" but no complaints on the quad atm

if it aint broke dont fix it

just got home from the Detail Rained most of it lol

ill go with that if it aint broke dont fix it.... would prolly save more $ that way