I'm a total newb at networking so forgive me.What I'm trying to do is create a private network for local file sharing but also have internet access. There is a WRT54G router connected to a satellite modem in a separate building, just barely close enough to connect from my laptop, which is what sparked my original idea to use my WRT54GL as an access point. If anyone can point me in the right direction, it would be much appreciated.
This creates a wireless client bridge from the wrt54gl to the wrt54g. The wireless signal is then repeated to a new subnet behind the wrt54gl, which now has its own firewall, DHCP server, etc. This is sometimes referred to as a WISP (Wireless ISP) router because instead of your router’s WAN port being connected via wire to the modem (ISP), you’re creating a “virtual” WAN port to the ISP over wireless. Users of the WRT54G cannot access the subnet behind the WRT54GL thanks to its firewall, yet they always have access to the Internet through the WRT54G.
Of course, this assumes the wireless signal from the WRT54G is strong enough to be reliable for these purposes (your description suggested this was questionable). You may have to do some experimentation regarding positioning of the WRT54GL to find the ideal location, one that balances the signal quality to the WRT54G and wireless clients of the WRT54GL.