As above. Thanks.

yes. a pci express card will work in any slot >= its own width. a pci express x1 card will work in an x4, x8, x16 slot, etc.

what xmokshax said is correct. Toms did a review back when PCIE 1st came out. they took a mobo with a modified bios and a x16 vid card, and ran benchmarks with the card at x16, x8, x4, x2, and x1 to see how the lack of bandwidth affected it. pretty nifty test imho, here is a link to the article. http://www.tomshardware.com/2004/1 [...] page2.html
Results? yes it is possible.

well, its quite interesting to see the result done by Tomshardware. it seems that pci-e 4x is just enough for current graphic cards.