The Linksys WRT54G runs Linux, and all the firmware has been GPL'd and now available for download.
Check out: http://www.linksys.com/support/gpl.asp
I see two things possibly happening in the immediate future:
1) Good: New tweaks/add-on functions, etc. for this model AP/Router.
2) Bad: New attacks on this AP/Router based on uploading modified firmware code into APs with default settings. I hope this comes with some sort of default WEP or WPA.