same problem here: I have windows Vista and Sprint PPC 6700

I followed your steps to modify the inf file and the driver seemed to have installed properly, but I cannot see it on the Sprint connection manager or the dialer.

Later, I followed your link to:
How to use or to reference the Usbser.sys driver from universal serial bus (USB) modem .inf files

but, I dont know what to do with that information???
Please help.