Installing dd-wrt is not that hard if you go step by step here
http://www.bitsum.com/openwiking/owb...sp?WRT54G5_CFE
I have done this firmware flashing with 2 Linksys routers already (WRT54G V5 and WRT54GL V1.1) with no problems
What version is you WRT54G router? V5 maybe.
*EDIT: If your ever wondering what DD-WRT looks like check out this screen shot.