Upgrading XPS 730

I am thinking of upgrading my XPS 730.

Current specs 32 bit Vista Ultimate

4 Gig Ram DDR 3 1333Gz

Nvidia GeForce GTX 280 1gig

Intel Q9550 2.83Gz quad core cpu

My thoughts are by

Installing 64 bit Vista and I assume that increasing the ram to 8 gig but not sure if i will need that much initially

Also by upgrading the video card, here I am totally confused, firstly would a 2 gig GTX660 be overkill so should I just get a better quality 1gig card ?

Secondly, Dell only specifies the PNY XLR 8 GTX660 I look on line and there are at least 2 dozen various makes of the GTX660 are they all basically the same from different manufacturers or will only some work with my XPS?

I use this as a games / all purpose desktop and apart from some parts of  Microsoft Flight Simulator I rarely have slow framerates although I don't play many up to date top end games either.

I have a limited budget so any advice or recommendations / alternative options would be welcome, If I have to choose what to do first should it be ram or video card?

Thanks

Don