I recently tried installing Xubuntu "Gutsy Gibbon" on an older laptop using a whole bunch of methods: the "alternate" Xubuntu 7.10 installer CD, the "alternate" Ubuntu 7.10 installer CD, the "server" Ubuntu 7.10 installer CD ... and they all failed. In all cases, the problem was the same. After the installer booted off the CD and moved through some preliminary information gathering, it would complain that the CD-ROM from which it had been loading was no longer mounted/found (Do you want to install the drivers from a floppy?).
A visit to the Ubuntu forums didn't really help... a couple other people had the same problem but with no solution. My best working theory at this point is that the problem is caused by the CD-ROM being an older LG device. There was a time where installing (some?) Linux would allegedly destroy (some?) LG CD-ROM drives. I think that this made a lot of developers paranoid and build kernels without support for many (all?) LG CD-ROM drives. Or not.
In any case, I managed to work around the problem and get Xubuntu installed. That's the good news. The bad news is that the system doesn't recognize the CD-ROM drive, but I was expecting that to happen anyway.
Here's what I did:
1. Download the "Minimal CD" version of the Ubuntu install CD--which basically does a network installation, sucking in what it needs over the Internet.
2. When you get to the point in the process that asks you if you want to install a desktop environment, indicate that you want XFCE/Xubuntu.
3. There is no third step.
It took forever to download the desktop environment, but it worked. It's a little interesting (and scary) that I didn't have this problem with Debian Etch, and I hope the next version of Ubuntu fixes the problem and/or the next version of Debian doesn't break it.