I have a ISA 2000 box being fed using Cable internet, and another backup ADSL internet connection via a wireless through a WRT54G box at another building that I use a bridge to poll into the server room so its connected to a HP Procurve 2524 24-port switch.
My setup is like this...
Building 1 on 192.168.1.0/24 subnet (VLAN2)
---ADSL---WRT54G>> to building 2
Building 2 on 10.10.X.X / 255.255.0.0 subnet (VLAN3) from WRT54G>> wireless link