... (without paying an arm and a leg for equivalent purpose Cisco hardware which would be overkill for hobbyist usage) ...
Silicium : a bit of unasked-for advice : ditch the p3 crap and buy a Cisco 3640. I went through all that garbage myself, only to waste hours and hours and hours on unreliable garbage. I can get a 3640 or 3660 for fifty bucks or less, so there should be equivalent options in Europe. My Cisco ran over two and a half years nonstop before I had to shut it down to add another network module. It goes so long without attention that I forget the IOS commands. All the "free linux router !" stuff is just junk.
Oh. Given a choice between a 3640 and 3660 (prices seem to be about the same these days) I'd get the 3660. It gets to be too much fun adding all kinds of other network interfaces. You'll eventually want the extra two module slots