Using old hardware to make a torrent box.

I build a small wiring closet in an empty closet in my house with my modem and router. I plan to also put a small machine to download torrents for me to.

The specs will most likely be crap I have in my basement:
Pentium III ~450Mhz and matching ASUS motherboard. Probably very little RAM, assume a single stick of 128mb. Generic video card, not even sure if it will be AGP. I'm probably going to have to buy a small harddrive around 20-40Gb. The machine won't have much cooling since it'll need to be quiet.

The features I'd like are webserver and torrent client+web interface. I want the most lightweight OS and software.

What are you suggestings?

>>13
I tried Gentoo once and couldn't figure it out. I'm not a programmer and I haven't the slightest idea what each of the CFLAGS do. I got tired and stuck to simple Debian with apt.

Also, I don't just want to put torrents in a folder and have them run automatically. I want a decent web interface that shows me completion, peers, status messages and simple controls. If you even used the HTTP interface for Azureus thats good enough.