Hey. I've been kinda having the same issues with my setup, so I've done some reasearch and figured out there are really two methods to accomplish this feat...
1- Go with a Linksys router that's 802.11g and get an external antenar with a directional projection pattern (just go to Compusa or somewhere and they have a whole aisle of them) and that should assist with getting it out there, unless you live in a bomb shelter... that's a fairly inexpensive method, and not too ugly looking.
2- The ugly method... you can get a Pre-N Router (the latest and greatest) and that should give you that extra distance... the PROBLEM is that for Pre-N to work, you have to have a Pre-N receiver as well, meaning for the Mac you'd have to attach a USB receiver to your beautiful system... blehh...
3- *bonus response* You could just get a verizon broadband card... expensive solution to a simple problem tho, but thought I'd throw it in as an idea.