BOOYAH! TAKE THAT!
Sorry, but I have GOT it fixed...!
The fix, you ask...
I set the MTU on the Ethernet from 1500 to 1492. It worked on both Macs, and now Software update, eBay work like a charm! I was surprised to find that A LOT of Mac users had the same trouble and mentioned eBay and Software update at the Apple forums.
So there ya go.....I'm back, baby!