well..i have old laptop too..centrino Pentium M 1.7Ghz
I make it as a download machine..also as an internet server..:D
Saving electricity bill, alot i think...:D
Rather than turn on my 750watt psu whole night just for download something..
Or you could use it as a portable media machine! Hook it up to your friends TV with a simple cable and viola!
Mind you, these days you can pick up 32GB USB sticks for pennies, and most modern TV's come with USB in, so that idea will be ancient soon.