I went through the process if installing a Ralink RT73 USB dongle to a Dell Optiplex desktop runing CentOS 4.4 a short while ago.
I recorded what worked for me on my web-site: www.coulterfamily.org.uk
(as an aide-memoire to myself if nothing else!).
Follow the PCs and Workstations
link to Linux
and then to Wireless
Thereon is a step-by-step of what I found (eventually) worked for me and at the bottom of the page are a couple of tables with a number of links to drivers and information that I found useful, especially links such as:
(general not just wireless) networking help
Hope that helps.