Deep C,
I've got exactly the same set up as yourself,(Pipex,XP, Speedtouch 330 USB)
I have absolutely no problems and I'm even using the drivers that were on the CD that came with the modem.
Mind you when I set it up I forgot to restart the PC before plugging in the modem. The thing flatly refused to do anything. I removed the modem rebooted the PC then plugged the modem back in, no more problems. Still no problems after 3 months.