If you can hold on a few months, ATI is coming out with a new revamp of its old external graphics card.
You will need an external GFX card. up to now they really wasnt worth it. But, ATI is (from what I have read) to release a GFX card for external use. They claimed to have fixed the issues with ext cards...we will see.
Price tag will be high from what I have seen...around $700
with that out of the way, if you have a ExpressCard slot on your laptop you can use a external docking plate and just buy any GPU you want for a desk top and use it. I had a set up like that several years ago when a ExpressCard slot was on all laptops.
here is a recent article explaining more about it.