Installing BYOND (Dream Seeker / Dream Maker) in OSXNOTE: This requires a valid Windows (7 or XP) installation disk or ISO.
Virtualbox is a program created to run Operating Systems (like Windows) inside of another Operating System (OSX).
This provides the best compatability for running Dream Seeker without having to duel-boot or reboot into Windows.
Overall this guide from start to finish should take about 15 minutes (excluding Windows installation time).
The following guide by Lifehacker explains how to install Virtualbox with a Windows VM.
After following the guide, you may install the Windows version of BYOND in the VM.
Virtualbox Download Page (Download for OSX)
Lifehacker Article (Setting up Virtualbox)
Enable 3D Acceleration (Optional)
BYOND Suite (Install the EXE inside the VM)