X16 and x4 slots

i baught a gigabyte h57m-usb3 ultra durable3 mobo it seems to me it has 2 pcie x16 slots but after a closer look and some reading,it now looks to have a x16 slot and a x4 slot,so my question is can I put a x16 vid cards in the x4 slot so I can run 2-x16 cards?

Its recommended that if you are going to use a single card,then put in the first PCI-E Slot.
However if you want to use 2 cards on it,then they will run @ 16x4x which won't perform well(compared to dual 8x/16x)

okay,let me start off saying thanks for the fast replys I am not,by any means,a tech. I am a gamer. I play all of the quake games and am getting into cod mw2. I baught a pc combo kit that had that mobo and an intel i5 duel core @ 3.33. I went and got 2-geforce gts 250's @ 1gig each and want to run them at full speed so what mobo do you recommend for the i5 and windows 7?

I should have added one other detail before, too. AMD will let you run their cards CrossFired in a x16, x4 - but Nvidia will not certify boards for running SLI that are x16, x4 because of the poorer performance/experiense the user will have.

I would look for a mobo with the P55 chipset that is CF and SLI certified because if it is certified CF and SLI then it will have two PCIe 2.0 x16 slots that, when both are populated, run at x8, x8. So to be safe look for:
1. P55 chipset
2. CF and SLI certification
3. Two PCIe 2.0 x16 slots that run in x8, x8 when both are populated

I am going to use 2 geforce gts 250's @ 1 gig each......but can return and buy 2 new cards that u think might be better than the 2 I chose
I am in no way a tech just a gamer that is trying to build a gaming machine to play q3,q4,q5 and CoDmw2. I bought a pc combo kit from newegg.I really want to run 2 cards so help with the deciding of cards and mobo....thanks.

i have an LG 23" lcd hd mon. and I have the intel i5-660

1920x1080 is the res.....sorry it took over a year to respond was a lil tied up