depends on what you got. anything less than a last generations high-end than yes it would be a really good deal. but seeing your specs it will be highly bottlenecked.
Sounds like a bargain. Just remember not to expect much from medium/high res dx10 performance. That seems to need more memory. Apart from that it will race through any game in dx9 except crysis of course. In general former high performance cards bought second hand for beans is a good way to go. Ive got 2 graphics cards from ebay that way.