Fedora Networking :: Dual NICs And Internet Connectivity On F10

I've just installed Fedora 10 to basically work as a NAS for another machine - but also serve a couple of web pages. After having alot of issues with network manager (with it changing the subnet so nothing would work), I'm now almost there:

I have two network cards connected in the server:
1) eth0 connects to a switch that ultimately connects it to the net (on a 10.0.0.* network)
2) eth1 connects directly into another server for backups (192.168.0.* network).

Now when I setup eth0, I get network access can ping/ update/ surf the net - absolutely no problems, but when I connect eth1 in - the net dies and nothing works, I can ping devices on both the 10.0.* and 192.168.* networks, just nothing past the gateway. I presume this is either a route or DNS issue, but am unsure about where its falling foul - both the resolv.conf file looks fine as do the ifcfg-ethx scripts.