If you only have a USB 1 port your issue is not just the slow WiFi, but a slow PC in general. While you may see a slight speed increase in your throughput with USB2, it will not be nearly what you think it will be.

You may want to post your full system specs, and when was the last time you installed a clean Windows setup? I'm thinking spending $100 on a fast used P4 system will do you much more good than looking to get USB2.