i haven't had the standby problem again since installing the softpaq, but i haven't really left my laptop alone for long yet either! i'm less bothered by that than having to reinstall it everytime anyway.
the p/n of the usb isdn adaptor is 321750-B31 if that is any help. my laptop isn't a compaq, its a higrade notino 2200. i think its quite an old isdn adaptor, the packaging says win 98, but on the compaq (hp) site there are updated drivers for win 2000.
i tried doing what you said and plugging it in after windows had rebooted, but it still didn't work and i had to reinstall it again! :(