more less the same thing.... unless u get a very good 1gb ram n mobo u might be able to hit 1000 CL4.....

basic rules for ram...

more capacity > more speed > tighter timing

imho.. just add another pair of 2x1gb ram since u are not gonna OC it (assuming u are running 400x8 for ur proc)

it always better to get back the ram of the exact model n brand to be added.... but if u really cant find it other brand ram of the same speed oso can be added actually...

well.... 2x2gb wud suit u better... afaik having more ram stresses the mobo n generate more heat....

just go for the corsair if u think the price is right for u

there are a few 2x2gb rams like team elite or crucial that is priced quite good iirc