Forum OpenACS Q&A: Re: VMWare
Bridged VMware is a breeze.
NAT'd VMware works and probably works well, but it does require some setup if you want the external net to get access into your NAT'd VM. (Don't get me wrong, NAT works trivially for connections from VM to net.)
For the router, you might want to take a look at CoyoteLinux or Mitel's (a.k.a. e-smith) firewall distribution. Stick a coyotelinux floppy into an old PC with two NICs and you have a router. Mitel is a RedHat derivate tuned for security and ease of maintenance. Both have been good to me.