Replying to Help me with buying a new computer

i don't know shit about computers so

http://www.costco.com/Browse/Product.aspx?Prodid=11327097&whse=BC&Ne=4000000&eCat=BC|84|4797|4798&N=4001606&Mo=21&No=15&Nr=P_CatalogName:BC&cat=4798&Ns=P_Price|1||P_SignDesc1&lang=en-US&Sp=C&hierPath=84*4797*4798*&topnav=
this seems like it has very good specs for the money, but some reviews complain about fan noise. would replacing the fan reduce the noise?

i see that it doesn't have a separate graphics card, would something like...
http://www.costco.com/Browse/Product.aspx?Prodid=11318665&whse=BC&Ne=4000000&eCat=BC|84|56671|4773&N=4017761&Mo=4&pos=6&No=0&Nr=P_CatalogName:BC&cat=4773&Ns=P_Price|1||P_SignDesc1&lang=en-US&Sp=C&ec=BC-EC10600-Cat56671&topnav=
and
http://www.costco.com/Browse/Product.aspx?Prodid=11318676&whse=BC&Ne=4000000&eCat=BC|84|56671|4773&N=4017761&Mo=4&pos=6&No=1&Nr=P_CatalogName:BC&cat=4773&Ns=P_Price|1||P_SignDesc1&lang=en-US&Sp=C&ec=BC-EC10600-Cat56671&topnav=
be compatible?

I don't see a firewire port, how should i go about adding that?

i also may want to add a soundcard cause i'm gonna get decent speakers. don't know what difference it would make, but what should i be looking at?

also would choosing xp over vista be good? i'm using xp right now and have no complaints. the only vista systems i've used so far only have 2gb ram at most, so it was pretty slow. but 4gb is suppose to be sufficient.