Yeah, it really depends on the type of people for whom you wish to host, and the features you wish to have. Things like stats require you to keep logs which can take up a lot of space on a hard drive. Also, player movements and physics calculations for shots require a good amount of RAM. I'd advise using a good computer with at least 512MB of RAM and a nice 30GB 7200RPM IDE ATA/100 AT MINIMUM. With 386/386, your bandwidth will be your prime conservation effort.
Your critical components, from my findings and playings, are RAM, CPU Power, and Bandwidth. I've played on a 486/DX33 server which had 128MB of SIMM RAM (Dual system) and it was ok ONLY because of the T3 line it sat on. I've also played on OC3 servers that SUCKED massive with over 1/4 of the total bandwidth ( almost an entire T1 line ) dedicated to it alone because it lacked the RAM needed because it kept logs for stats. Also keep in mind your OS. Linux Servers tend ( not always are ) to be better servers due to their lower overhead than windows. BeOS or *BSD may be better but there are no ports that I'm aware of.
You really don't need a lot of bandwidth for each player if you set rates to decent levels and tell the players. Most people don't realize that in half-life you can set your rate to 5000 - 7500 on any broadband connection and get a decent ping, AND it's more fair to dialupers ( because all requests are delt with in a first-come first-server basis, the server will offer up more packets to broadband than narrowband players, which results in CHOKE for the dialup player).
Those are just my thoughts