I had a tough time too - it turned out the slingbox even though it is DHCP and a poweroff and power on of the slingbox does not change the setting.

There is a small button on the slingbox that makes it reset. Hold it for 5 seconds.
http://us.slingmedia.com/object/KB-005036.html

That's got mine working on the lan.
Although it works fine on the lan I am having some issues about viewing it over the internet.

I think I have the port forwarding setup right now and I will test it by going up to a coffee shop later.

Thanks for the tip. I'm none too thrilled with the reliability of this box. Had almost everything going only to find all of the wired PCs in the house dropped off the LAN overnight. On to plan B - ripped it out to try another day :(