Linux 2.6 has changed significantly what modules need to do when loaded/unloaded, and to a certain extent how serial drivers operate (mostly to do with timers/queues from what I've learnt so far), because of this the pctel drivers you have there, will not work with 2.6.
I've got the same problem, having a builtin PCtel modem in my laptop. Not having this working is incredibly irritating, and so as I can't find anyone else having ported the drivers, or even attempting to do so, I'm willing to give it a bash myself. I do however, have very very little experience with writing kernel modules or serial drivers, so this is going to take awhile while I get up to speed on how 2.6 serial drivers need to operate.
All that can be suggested at the time being, is going back to 2.4, as I have had to. If you happen to use Gentoo or compile alot of software, this can actually be a lot less frustrating due to tiny changes in headers and so forth in 2.6 meaning alot of stuff just doesn't compile straight out of the tarball.
Hope that helps ]
