I currently run a windows 2003 sbs. While this has some wizards to help you configure it, it still is very much possible to administer this as if it were an ordinary windows server 2003 server. Is it true that this is not possible on windows sbs 2008? For instance I read somewhere that you cannot configure DHCP yourself, but that you must place a router with an IP address of 192.168.x.1 between your WAN and the server.
The limitation you list (having a router) is because SBS 2008 no longer supports being an edge device, thus what you say is correct.
However, you can still administer it exactly the same as you would a normal 2008 server. You still set it a static IP address, and configure it however you want.
The thing you're talking about is the Network Setup Wizard. It's generally a good idea to run it anyway, and when it gets to the stage in question, it does a uPnP search on the network for a consumer-grade router. If it doesn't find one, it simply gives you a list of ports it expects to be forwarded and you set it up yourself.
You can definitely configure DHCP yourself. In fact, it demands that you disable all the other DHCP servers in the network when you run the network wizard. I had a bit of a problem with this because it kept finding ITSELF as the DHCP server and telling me to shut it off (which of course, I couldn't) but this was just a rogue routing entry and was easily fixed.
A few other things to note about SBS 2008 that differ from 2003 that weren't really in your question (that you might want to know anyway):