I had the same problem... had too many machines, wanted to run linux but didn't know why.
Here's what i did:
Turned one machine into router/firewall
This is pretty cool.  I picked up 
Clarkconnect, which is software put out by Point Clark.  The software is a really trimmed down and locked up version of Redhat 7.1.  It has great features, such as web administration and an apache web server all setup.  This software was the easiest thing i've EVER installed.  Right from the install, everything's set up and working.  Great way to make good use of a machine if u ask me... everyone needs protections from the internet.
I've also set up file server.  Since i run an FTP server, moving the traffic from my 2k box to a linux box is great for security.  The file server is just cool to have 
 
I'm also tryin to set up a mail server, but i think that may have complications out of my hands.  That machine runs Mac OS 8 though.
Just some thoughts...  It's a great way to learn linux, i don't know if u know it already.  I'm still a n00b...  but i'm learning