(updated September 13, 2011)
Escape Velocity is a wonderful role-playing/action/strategy/trading game for the Macintosh made by Ambrosia Software.
The best way to play Escape Velocity on a Windows PC is to purchase Escape Velocity Nova (part three in the series), which has been ported to Windows. It costs thirty dollars. The scenarios of the first two games can then be played as plugins. These plugins are totally free! For help with this, stop by the Escape Velocity forums at Ambrosia.
If you simply must play the Escape Velocity games as they were originally released for Mac OS, you should use a Macintosh emulator. The best emulator to use is Basilisk II. We have a Basilisk II Setup guide. You'll need to follow the directions to set up the emulator and then install Mac OS 7.5 (free). You can then download and install Escape Velocity.
We have a busy support forum that can answer your setup questions.