Hp motherboard questions

Hey everyone, i just purchased this HP A1740n model computer (http://h10025.www1.hp.com/ewfrf/wc/document?docname=c00838760&cc=us&lc=en&dlc=en&product=3340229&dlc=en&lang=en)
Those are the stats ^ and these are the motherboard specs (http://h10025.www1.hp.com/ewfrf/wc/genericDocument?lc=en&cc=us&docname=c00379422) Anywho im fairly new to computers dont know a whole lot and i got some questions for anyone nice enough to reply to them! So my first question is i want to upgrade my video card and ive been looking at the 8600gt xxx seems to be a great card for the money and i wanna know if my motherboard can support this card i belive it can with pci-e but i wanna make sure! (http://www.tigerdirect.ca/applications/searchtools/item-Details.asp?EdpNo=3048552&sku=P450-8650) Also my computer came with a stock psu of 300 watts, should i buy a new one for this system? if so ive been looking at this one its a cheap price and i think should do the job (http://www.tigerdirect.ca/applications/SearchTools/item-details.asp?EdpNo=541439&body=MAIN)
And last but not least is the memory, i belive my motherboard supports the maximum memory of pc-4200 533mhz. (correct me if iam wrong please) The questions i have about the memory are: Can my motherboard support 4x 1gb of ram? Can my motherboard support DDR2-Dual channel ram or just DDR2 regular ram?
if i can only get regular ram im gonna get these (http://www.tigerdirect.ca/applications/SearchTools/item-details.asp?EdpNo=486747&CatId=1649)
If my computer supports dual channel ram i plan on getting these
(http://www.tigerdirect.ca/applications/SearchTools/item-details.asp?EdpNo=1169989&CatId=2364)

Anyways whoever reads this and responds much thanks to you!!
-Cheers!