A simple network

I'm new to Linux and with what I've seen so far (1 night downloading, 1 night installing) I'm impressed. Is it possible to hook 3 or more PC's together using their serial port with Linux in order to make a simple network? Where do you get such cables?

Dos & Linux

How can I download .tar and .gz compressed files on a Dos system copy them over to my linux system and uncompress them? Is the uncompression built into unix? Also can I interlink my Linux and my Dos system? (my modem is on my Dos system).

xt?

Can debian Linux run on an xt? If not is there another linux that can run on an xt? a http: link in the right direction would be appreciated.