Dear Phil, Thank you for reaching us at Creative Customer Support Services again; we appreciate the opportunity to assist you.
With regards to your reply, I understand that you are actually dual-booting on your computer. This, I believe, may be the problem here. I would not suggest that you uninstall either one of the OS on your computer but we actually do not recommend that you install your sound card and dual-boot on one computer.
If you might want to try, you may remove your sound card and install it on another computer running on the Vista x64.
Do you face the same problem? I certainly hope the above step(s)/information will resolve your query/problem completely and I look forward to your favourable reply soon. Do not hesitate to contact Creative Customer Support Services again should you have any clarifications in future.