And to answer your specific questions:

Can the empeg be easily modifed to access an NFS file system when "at home" so that it has access to the entire song library? I imagine this would require two databases: NFS directory available and not...

I don't believe there is support for this in the player software at all. There's a lot of hard-coding in the player software to only access the local drives for its playback. It's got a lot of code involved in the caching algorithm, and it has to control drive spinup and spindown, for example.

Has the empeg player software been ported to i386 so that I can install similar software on my Pentium "library" machine?

No, and it's not open-source so there's not a lot of likelihood that'll happen.

Can the empeg be opened up and connected to 3.5" IDE drives so that I can get enough disk space?

Well, that's an interesting question. The player's power supply won't support desktop drives, and they won't fit in the case. But if you were choosing to build a home player using the guts of an extra car player, and you supplied your own power to the drives... hmmmmmm.... Don't know about that one, no one has ever tried. I'm really curious to know what Hugo has to say about this one.

Would 48bit LBA be an issue? Will this ultimately be an issue when laptop drives exceed 136GB (or whatever the magic number is)?

Yes, that will be an issue. At the moment, you can only get up to about 128gb per drive because the player's kernel is an older Linux version and doesn't support drives bigger than that. However, we happen to have in our community the guy who wrote the Linux IDE drivers (Mark Lord), so if anybody can code a work-around, it'll be him. If you're serious about doing this, he might be the guy to talk to.

What is the rest of the group doing for a dedicated large-library mp3 player?

I think most people are just using off-the-shelf programs on their desktop PCs.