The Speedbooster isn't anything to do with signal strength, it's a compression technology that is intended to improve on the bog-standard throughput speed of 802.11g and offer an increase of 35%-40% over 802.11g (at least theoretically that's what it's supposed to do

).
However, in order for your router to use it, your Wireless NIC or USB adapter needs to be a compatible model, such as the WPC54GS.
Saying that, if you changed the firmware on the router to use dd-wrt, you can increase the strength of your signal by playing around with the Transmit Power Adjustment settings of the router, and can increase the power from the default 28mW. The dd-wrt forums suggest going up to 100mW is harmless but should increase your signal strength.
If you eliminate configuration issues, this might be something to consider.