You don't need a really good gfx card. Like most RTS games, they use alot of CPU power, so upgrading your CPU as well won't hurt. Unfortunately you've got a laptop which is just not worth upgrading. So If you want something better you want to get a PC, besides you can upgrade it unlike a laptop.
What you need is a fast dual core CPU and overlcock it. But personally I would prefer a quad core and overclock to 3.6Ghz or something. Gfx card wise I think a ATI HD 5770 will do you fine.