I saw there were no posts or tips here, so I decided to try installing and running Portal: Prelude and let you know how it went. I just played through version v1.1.5 of the game. I found that it's easy to install, and it works just as well as Portal itself (which is perfectly, on my machine). Here are the steps to install Portal: Prelude.
- In a new bottle, install Steam and Portal. (See their respective entries in this compatibility database for info on how to do this.)
- Run Portal at least once. Make sure it's working. If not, troubleshoot Portal until it works before going on to step #3.
- Download the installer for "Portal: Prelude."
- If it is still running, quit the bottle in which you installed Portal.
- Choose the "Install Unsupported Software" option. Choose to use an installer file and select the "Portal: Prelude" installer you downloaded.
- Install "Portal: Prelude" into the same bottle where Portal is located. You can accept the default file paths the installer suggests.
- Run Steam. You will see "Portal: Prelude" appear as a separate game in your "My Games" list. You launch it through Steam, not from within Portal.
For me, "Portal" and "Portal: Prelude" both experience an enormous performance boost if you add the game launch option "-dxlevel 80" (without the quotes) to Steam before launching the game. Info on how to set a game launch option can be found at http://supportwiki.steampowered.com/wiki/Setting_Game_Launch_Options .
I'm using CrossOver Games 8.1.4 on Mac OS 10.6.2.
I hope this is helpful for someone!