Got a site to site VPN working with ISA 2006 to Linksys WRV210 as follows
WRV210 192.168.1.x <-------> ISA 2006 192.168.5.x
After it's connected, I try to ping 192.168.5.99 from 192.168.1.102. it shows up in the ISA logs as being allowed, but I still get request timed out on the originating side. So, ISA doesn't think it's stopping it, but I'm still not getting a response. If I VPN into same ISA server, I can ping 192.168.5.99 just fine.