Summary: If you're thinking of ordering this for use with third-party open-source firmware like Alchemy or DD-WRT, you're out of luck. The router that now ships is "WRT54GS v.5", which is vastly different from v.1, v.2, v.3, and v.4. Version 5 does not use Linux-based firmware and is therefore not flashable with third-party firmware. You'll have to find an older version on eBay etc.
Summary: I bought a WRT54GS v4 wireless router on 10/30/2005. It does not work by just following CD setup instructions. After talking to Linksys technique support, I manually configured the router in router configuration pages. The problem was both Verizon DSL modem router and Linksys router use the same default IP address. After got DSL working, I found that my PC is always talking to buydomains.com which slows down every command I entered for at least 20 seconds.