Have you two guys downloaded the latest 7250 HANDHELD code - not the Desktop Manager code, for your BlackBerrys. It should be on your carrier's web site. Download it and I bet is has the modem drivers there.
If you haven't done so, please read [User] HOWTO: Use BlackBerry As Modem For Laptop!
- and read the entire thread. I am not sure anyone has gotten a 7250 to work as a modem.
Before you waste a lot of time, please consider that.