A very smart investment if you're set on getting an 8800gtx, IMHO. Good luck with it. I'm contemplating getting one myself. I've got the TPII 430, which has a total of 34A on the two 12v rails. Theoretically, I should be fine. Then there is the issue of getting it into my Antec Super Lanboy case. I've seen pictures suggest that it is possible but, measuring it myself, I sure don't know how without taking out the HD cage.
At any rate, have fun upgrading!