You should try changing channels. As Grant suggested, there are only 3 channels in the 2.4 GHz range, so if you're on 6, try 1 or 11. The problem with going to the 5 GHz band is that it is much more affected by obstacles and has a much shorter range.
I bought one of these around Christmas (amazingly, it was only $10 with the rebate--if you subscribe to newegg's email, it may come up with a promo code at some point that will reduce the price signicantly.) It is an N router, which means it's much better able to receive and transmit signals that are multi-path, that is bounced all over the place, as they are on the 2.4 GHz band. I have it pretty far a way from the Mac with wireless and I'm rarely seeing it dip much below its highest Transmit Rate of 130. A G Router will be far less effective, especially in a crowded environment.
http://www.newegg.com/Product/Product.aspx?Item=N82E16833320168
Even at $40, it's an excellent router.
You can use the stock Asus firmware (aka operating system) or a much superior one called Tomato can be installed without a lot of trouble. If you get one of these and want to use Tomato, then post back to this thread.
Just a tip: I installed Tomato immediately, so don't know if this option is present or not with the Asus firmware, but if it is, keep the channel bandwidth at 20MHz. At 40MHz, it will pick up too much interference, and performance will be terrible.
You can only really accurately know what your real Internet speed is by connecting with an ethernet cable, instead of wirelessly.