Connect them in this order:
Modem --> Router2 --> Router1.
Router1's WAN port should be connected to any LAN port on Router2 - this will firewall Router1 fully from Router2, but still give it 'net access.
Leave Router2 at its default settings; and set Router1's WAN IP address as a DMZ (reason being that you don't want Router2 to do any firewalling of traffic that needs to make it to Router1.)
Change the LAN IP address (and DHCP range) on Router1 to a different subnet. IIRC, Linksys is (by default) a 192.168.0.x LAN; for simplicity, change Router1 to run a 192.168.2.x LAN. Note: you will need to do this with Router2 not
connected to Router1 yet! Otherwise, it'll be quite unpredictable which router you'll be logging in to.
You should still be able to admin Router2 from a machine on the 'private' LAN, without creating a 'static route' in that routers config.
It'll be a little tricky to set up, it may be fussy, and this will create additional potential points of failure - if things go pear-shaped, it'll be not the easist to troubleshoot.
One other thing you may want to consider: if you have an 'older' PC laying around, and a couple of spare NICs, you may want to consider setting up a Smoothwall, and using that as your gateway device. You can still use the '54G's that you have (in AP-Only mode); Smoothwall will handle all routing duties.
"Guest" network is Blue; "private" network is Green. Blue is fully isolated (one-way) from Green: nothing on Blue can 'see' the Green network. And, it's extremely stable. Mine is rebooted only for updates (once or twice a year), or (since it's not on a UPS) power outages.