Are you getting 404 errors when you try to update Ubuntu 8.10 beta/release candidate? So am I.
Annoyed because most of the resources on the internet are dismissive, unhelpful, and kind of snide? Me too.

Now, in spite of my continued assertion that I am something of a linux expert, I actually am not very savvy when it comes to fixing parts of an OS that just don't work, but I'm not afraid to root around... especially when it's just a virtual machine I'm mucking with.

So, here's what fixed it for me. I picked "Main Server" instead of "Server for the United States" which was the default in the virtual machine I downloaded. This prompted a distribution upgrade for some reason, and after three hours and a reboot, update-manager was working for me again.

Try this for yourself. From your desktop, choose System --> Adminstration --> Software Sources to launch the Software Sources application. Pick something else from the "Download From:" option box. It'll look something like this, (especially if you're using the hotter-than-hot dark human look).

Anyway, It's Fixxored.
Linux is so easy.

(FWIW, I'd happily entertain discussion about what really was/is the problem on this here blog, if any one is in the mind to share.)d