Moved out of HnS thread as this has nothing to do with that topic.
I do not think it is possible. I think you just have to boot from it. Hence being a LiveCD. Why must you deny access to your Vista drive. Just dont click on it...
NeoGrub can't really be used to boot from CD (technically it can, but it's broken). But when you hide a Vista partition, the hiding persists until you use NeoGrub to boot into it.
So you can create a new entry, something like
Code:
title Prepare to Boot from CD
hide (hdx,y) # For all vista partitions
reboot