Tossing this out there, you may already be aware:
Your laptop should support G as well as B, so getting a router that does G should work.
While yes, there is the obvious speed issues between N and G, it likely won't make much difference unless you either have:
1, the need to do massive file transfers between another N connected or 100mb wired computer or,
2, you have a network connection to your ISP that exceeds the speed of your 54mb/s G wireless connection.
Faster wireless speeds won't speed up your connection to the ISP.
I think you'll find that most N routers have some backwards compatibility with G at minimum.