i wouldn't do it on a wireless connection, get any ati chipset card w/ 128+mb of ram you will me fine... i would definately get a router if your currently dont have one.

also scan your box for spyware/virus make sure you have the most updated clients for your games, all win patches, and latest vid card drivers. that should do it.

and by the way starcraft should never be slow unless you have a shitty connection or the server sux balls (that game came out like 10 years ago and runs perfectly on shitty specs)