Like many people I was hoping that Vista SP1 would fix the issue with Views in Windows Explorer changing randomly. But alas, it didn't. Gee, must be a big bug.

Anyway, there is a registry hack that fixes it - sort of. It doesn't actually fix it, rather it just sets all the folders undefined, which in effect will keep them at the current view.

To enable it you'll need to add a registry key, amongst other things. 

The full instructions are here on the Vistax64 forum, and includes details on deleting all the existing settings first. (BTW despite the x64 name, this works on both 32 and 64 bit versions of Vista)

And as usual, any registry changes are all on your own head.

(I was alerted to this by someone, but I can't remember who. So I can't link to them here... sorry)