Half Life Opposing Force port?

I was browsing Dreamcast Haven and I went over to their Downloads section and they had a Opposing Force download. Curiosity got the best of me so i downloaded it (of course I have the PC version :)) well anyways I unrared and burnt it and poped it into my DC. Their were 2 modes theirs, Opposing force and of course Mission Failure (A modded campaign with some adult themes). I played Opposing Force and it worked like a charm, even saving, but at times the game got laggy and eventualy crashed (May be a problem with my DC because it happened with Headhunter but it didn't crash). So is this legit or illgeal?

it must be a modded version of the leaked Half life commercial port, so yes its illegal.

wow, on a first glance you would never figure, although the first part dosen't show up when the helicopter crashes and stuff, it just starts you off at the med bay.