Neil B: I checked the wmiprov.log logfile you mentioned, I also have it and there were lines for "Impersonation failed" and "WDM Call returned error 4200" etc, but the latest one was for today at the exact time I turned my computer on, and I don't even have my Pulsar installed at the moment nor has there been a crash, so I guess this is just something that happens during every bootup. I don't think it's related to the problem, imho. On the other hand, the IRQ sharing situation you have is very similar to mine, the only difference is that I have the newer ICH8 USB Universal Host Controller on my motherboard.
I definitely do have my motherboard audio enabled, since I use it for gaming etc (yes, I know I should have a dedicated DAW, and trust me, wouldn't like anything more, but a poor student can't afford two powerful computers). I'm going to re-install the Pulsar today and disable the built-in audio to see if it helps (I can always stick in my old SB Live for gaming

Cheers,
Timo