The easiest thing would be to go to
http://www.borisfx.com/media100/ and download the 14-day trial of the latest software. It runs fine on Mavericks, and will install all codecs, etc, you need.
Only thing to watch out for, is if you open a project, programme, or bin file in the latest version of Media100 and save it (or if auto-save is switched on when you open it, and the system saves it for you), the newly saved files can't be opened on older/earlier versions of Media100.
However, I assume you're talking about Quicktime files in the Media100 codec, so you can just open them with Quicktime.
One tip - Quicktime X will not play back videos that use the old Media100i codec. Quicktime Player 7 will. You can download Quicktime Player 7 from Apple's website here:
https://support.apple.com/kb/DL923