[kretara]

IMHO the B&W would word just fine. All you will need to do is make sure you have around 1GB of RAM in it and it runs pretty fast. I have a B&W that I upgraded from G3 350mhz to G4 450mhz, gobs of RAM and newer HD and it still runs 10.3 nicely.
I don't know about a cube for a server. Cubes are great, but they are still fairly expensive. For the price of a Cube (in the States) you could buy a Quicksilver. Plus the upgrade ability of the Cube is missing. You will be limited to only 1 HD.

I know that this is a Mac forum and all but depending on what you will be doing with the server you might look at an AMD/Intel type PC running Linux. I've got two old Dell 450mhz running Debian and they are very fast and were free.