Updated: Moey Labs also has a great write up on this: Using a Virgin Mobile Broadband2Go on Mac OS X
I just got my Virgin Mobile Broadband2Go MC760 modem working with OS X, without the included software.
The modem worked with my older 2008 MacBook, and now with my 11" MacBook Air; both under Snow Leopard 10.6.6. I do not like the software though, if only because it needs admin privileges every time it tries to connect (so if you have spotty coverage and need multiple attempts to connect, you will be entering the password for those privileges often). Now, with it configured in the Network section of System Preferences, the lame manager is not needed.
Here's the link, thank you Kathy E. Gill, whomever you are! :) Virgin Broadband2Go : Service OK, Set Up A Pain
The key for me was to change the Vendor and Model in the 'Modem' pane of the Advanced section.
Cheers