I did indeed find the solution, although I don't think it will help you (at least, not directly) unless you're using the exact same model of laptop as me (mentioned in my first post).
Basically, Fujitsu stopped releasing driver updates for my laptop after Vista launched, which is just smashing considering it hadn't even been on the market a year. Luckily, they released a new laptop which has practically identical specs, but is 'designed for Vista'.
When I looked at driver updates for it, there was a patch that fixed a hard drive caching (or lack-of) error, but it was literally only for Fujitsu laptops.
Anyway, that fixed my problem.
I can't do a direct link to the patch, so if you want it you'll need to go to Support - Fujitsu Siemens Computers, go to the downloads section for the Amilo Xi 1554, choose Vista as your OS, and it will be listed under the 'Application - Service Patch' heading as 'HDD Caching'.
Good luck, hope that helps!