Dual Routers and Network Security

[Tricky]

I have purchased a new router and therefore I now have two routers, I have decided that on my main wireless network I am going to run WPA-PSK, but my wife's laptop cannot keep a connection on this but is fine on WEP. So the idea is that Router B (linksys) will run WEP and router A (Zyxel) will run WPA-PSK.

I have the following:
[Internet]-->[CableModem]-->[Zyxel (RouterA)]-->[Linksys RouterB]

I know I can run NAT on both connections therefore stopping clients on network A from seeing anything on network B (Different IP Networks) because of Double NAT'ing. But I want to stop clients on network B (connected via WEP) from seeing clients on Network A. The only thing I want clients on network B to see is the route out onto the internet.

As I've just purchased my Zyxel I want this as the main day-day router as it offers many more facilities - the Linksys will be turned on when needed and hardwired into Zyxel.

Am I barking up the wrong tree completely and cannot secure network a (clients) from network B (very hackable!)

Thanks!

[SMHarman]

Why don't you put the linksys router in the dmz of the zytel? That should do the trick.