Can i buy one of the expansion packs without the original GW?

The reason im asking this i because i was wondering if it would be cheaper just to buy an expansion pack without GW prohecies

I.E. if i bought GW nightfall without Prohecies will it work?

also can someone tell me the requirments for nightfall

Guild Wars: Prophecies, Factions and Nightfall are all stand alone products that can be combined. So yes, both Factions and Nightfall will work without Prophecies.

The up coming Guild Wars: Eye of the North is a true expansion and requires one or more of the above.

Edit: System Requirements

only EXP is GW:EN which hasn't being released.

NF and F are seperate games but can be linked to a single account.

it's an expansion, by definition you need one of original games. This is stated plainly on GW.com, and especially now, the original is much cheaper than it used to be, and Factions is going that way quickly too.

factions and Nightfall are not expansions. They, like the original, are stand-alone games. They can be merged on the same account.

Yes.