Just wanted to put a note on the web (as no doubt Google will hit this…) for pepople having the same issue that I had…
When trying to mount a Trucrypt (using version 6.3a) volume on XP at work, I’d sometimes get a BSOD with the line like IRQL_ERROR_GREATER_OR_LESS_THAN.
Anyhow, I think I narrowed the culprit down to the Microsoft Virtualisation Application Client.
I disabled the services and Truecrypt seemed to work no problems. Then I uninstalled it and all seems fine currently. I’ll post if it doesn’t fix it completely or whatever but so far it seems like it was a conflict between MS software and Truecrypt.