can anyone tell me if a Seagate Momentus 2.5 inch XT ST95005620AS 500GB will work OK in a desktop PC as all references I can find indicate its for laptops
IMHO, the drive you're considering has all the disadvantages of a HDD and few (if any) of the advantages of an SSD. It's a solution in search of a problem.
It's a great drive for general use. I've had two of them. Don't listen to ram. As Hawkeye said, you'll need an adapter, it won't come with one. They're like $5 on Newegg, though.