Did no-one look at the sig of OP's rig?
Gaming wise Phenom is a waste, with its issues and lower performance to that of Intel your X2 will suit you fine for a while yet...
Adding a second GPU will not help your cause if you have a small screen ie 19" as SLI only proves usefull on high res's. So i believe that to be a waste also.
Case depends on what you have now ... but the Antec900 will do you for a while.
and 24" depends on what you currently have if its small low res then this might be the goer... i love mine
Dell 2407HC