OP, I've got good news. I just successfully tethered my Verizon 8830 using the USB cable and I'm posting this using that connection.
What I did was download the VZAccess Manager for Mac which can be found on the Verizon Wireless website. They say the BlackBerry 8830 is not supported but I just installed it with no issues. It definitely seems faster than using the 8830 as a bluetooth modem.
Here's the link for the software for any of you Verizon Wireless BlackBerry users who want to tether with the USB cord in Mac OS X:
VZAccess Manager
I chose Mac 10.5.x as my operating system, PDA / Advanced Device as my device, and Motorola Q as my hardware. I know it isn't anything close to the BlackBerry but the software is the same for all devices.