First off, welcome to the dark side 😉
Do you know how the project was brought into the Avid? Was the project brought in as DV resolution (meaning it was downconverted, and you are offlining the project)? If it was you should have no problems. If you are working on HD footage, I’m not sure 4.6 will support your project. HDV was not supported until 5.0 (on the PC side – I’m not sure when it came into the Mac side) You might want to poke around the Avid site and search for a document called ‘supported resolutions’….
Mojo adds 1)component input and output (via Avid approved cables you need to buy from Avid), and 2) processing speed (plus the ability to upgrade firmware via software updates…)
If your project is DV resolution, and does not have a lot of layers and/or FX, you could probably get along without Mojo. If you do have multiple layers, lots of eye candy, you could still get along without Mojo if your willing to put up with render time.
HTH,
Jon