Graphics Power-supply/video-card problem

ok, i will put is as simply as possible
i own a Dell 9150, its power supply has 12v rails and everything, and is 375w
i have just bought a leadtech 7900gtx 512mb, and the packaging says that 325w is the minimum power requirement. but this still means that it will run right ???
i have no clue how to install it onto my mobo
and where to connects the power cable i got with it to, if you do suggest a better powersupply, them is it possible to use 2 (350w each ?) how would i set that up, and would i need a new mobo

i am also worried that i will kill it, if i install it and there is not enough power

thanx for any help