Nathan, pleased to see you've come over to investigate. Don't get me wrong, I am a big fan of Vector Linux but like many other distros it needs a lot of work to get it up and useable as a server, SME works straight out of the box.
My advice to you would be to bang another NIC into that box, they're pretty cheap. My setup is as follows :
Motorola SurfBoard Cable Modem to cheap as chips router then my 2 desktops behind router along with my SME box. I did have my SME box on the DMZ at one point but that was more hassle than it was worth. I am forwarding first 2000 ports to the SME Server as I'm confident that it can look after itself so security not an issue and that pretty much sums it up.
It now hosts my domain and all mail for that domain and is my local fileserver for my LAN. VPN access and everything work 100% fine.
Your wireless requirements may be a problem but I can't say as haven't used wireless yet. You could do a little search through these forums for anyone else that has used wireless and see what they have experienced. I just though that this would be a better bet for you as it's very easy to setup and administer.
Hope this helps,
Arthur