I changed my home network (router, cable modem, etc) and I can no longer connect to the Slingbox. Do I need the original installation disk to do this?
You don't need the disk. You probably do need to reset your Slingbox. Have a look here:
I was told by Slingbox that all software can be downloaded and an install disk is no longer provided.
Yep. You can download the SlingPlayer program (Mac or Windows) along with PDFs of the original documentation that was in the box.
For user guides and help go to support.slingbox.com and look for this thing on the right side:
Pick your model from the drop list and you'll find lots of information about your Slingbox.
For the Windows software, go here:
Hope this helps,