Ultimately, I think the problem is that the Slingbox isn't able to get a DHCP address from your Linksys WRT 350N router. I looked up your router's support page (http://www.linksysbycisco.com/CA/en/support/WRT350N/download) and saw that the most recent version is Ver.1.04.4. Are you sure that you're not using the DD-WRT hack replacement for your Linksys? If so, I recommend in trying to get support from DD-WRT techsupport (http://www.dd-wrt.com/site/support).
In anycase, I'm not sure how you were able to get access to your Slingbox without a DHCP server with your laptop. However, if you were able to get through the setup process but its hanging on the fouth step, then I would recommend quitting the assistant before it hangs. Once you've quit the assistant, connect to the Slingbox, pressing (Alt+O) and click on the Information tab. There under Identity subsection, you'll see the MAC address. You can use this information to create a reserved DHCP IP Address on your router.