Thanks Dave, for your response.
You're right; I had no luck at all getting the card to work during the install.
Just in case there are other frustrated Vaio PCG-N505 owners out there, it seems that mysteriously, the ethernet card won't work under Linux under IRQ 5. (Strangely, it shows up under Windows98 as using IRQ 5 and appears to work just fine.)
At any rate, if you can install via some other method, then add "exclude irq 5" to the config file and everything is happy.
A networked Vaio owner, -John
PS. I initially discovered this from http://www.ifb.co.uk/~liz/n505.html which by the way is a very useful page. It appears that it's not just my $35 10baseT pcmcia card--ethernet cards, IRQ 5, and Vaio N505s don't seem to mix well.