Upgrading My PC

[nineclicks]

So i want to upgrade my Mobo processor and ram, rather than building a whole new computer. But ive never actually chosen the parts for a computer before so i dont know exactly what im doing. so far ive picked these:

GIGABYTE GA-P35-DS3L
Intel Core 2 Duo E8400 Wolfdale 3.0GHz
G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500)

and, because my PSU is only 300watt this:
Rosewill RX750-D-B ATX12V v2.2 & EPS12V v2.91 750W Power Supply

basically im just worried about compatibility. and just had a few general questions.

first off i wanted to know if im over, or under doing it with the PSU. i want to be able to add a hard drive or something if i need to. ive already got two optical drives and an ATI Radeon X1050 video card.

also, do i need 64-bit windows xp or vista in order to utilize 4 gb of ram?

and in general if any of those parts i picked arent the best choice please let me know.

thanks for any help.

edit: by the way im not interested in overclocking or anything like that, if it makes any difference.

[ApPy10]

750 watt psu is too over. maybe a 450-500 watt psu would be a better choice & will support your requirements. Check here Power Supply List

[nineclicks]

what are the disadvantages of going too high with the PSU? i figured it would keep me prepared for a new optical drive, more hard drives or higher powered video card if i eventually choose to.