Flitting regularly between WinXP and OpenSUSE 10.2, I today booted into OpenSUSE and found mount problems with the ntfs partitions. Fortunately, I came across the acvice to ensure that windows had cleanly closed before anything recommending kernel surgery, and indeed restarting and then carefully closing WinXP did the trick and I'm back in business.

I do wonder, though, what exactly happens (or rather, I presume, does not happen) to the HDD when WinXP crashes that means I cannot properly mount the ntfs partitions using ntfs-3g? If restarting and closing Windows was not an option, how would someone get round it?

With Windows, nothing would surprise me.

I would simply put all shared data on ext3 partition(s) and use something like ext2fsd to access the shared data from Windows

I believe XP marks the partition as active and if XP crashes that bit is not removed (firefox does the same thing by creating a session lock file in your profile). As a safety feature, ntfs-3g will not mount the partition if it is still marked active. However, you can force an overide with:
Obviously, change /dev/hda1 and /mnt/ntfs for your own setup.