x64 beta - lost access to my C drive

Hi, I've got a bit of a problem with the x64 Beta of Windows 7 which has got me stumped. When I tried previous builds (including the x86 version of the Beta) it installed fine on my second hard drive in my laptop (Drive E - I have partitions C: and D: on my main hard drive, which runs Windows Vista x86)

But when I install the x64 version of the Beta on Drive E, after Windows 7 boots (which it does fine) then the drive that Windows 7 is on shows in "Computer" as C: - my D: partition also shows up (and is correct) but my Vista drive does not show at all. Does anyone know a way around this? When I install 7, I just select Drive E to install on as normal, so not really doing anything differnt, except, of course, you can only install the x64 version by booting off of the DVD - whereas when I install the x86 version, I always start setup from within Windows.

If I could resolve this it would be great - I have no problem with installing 7 again if needs be. I should also mention that Vista still boots fine from C.
Thanks for any help

Its ongoing and has been posted a couple of times already.
Open the Administrative tools.
Open Computer Management open Disk Management.
Assign a letter to the Vista drive.
Your Windows 7 will now show the Vista drive.

Thanks for the response,

I take it there's no way I can make my Vista drive show as drive C in Windows 7 then? This is how it used to show in previous builds, with my Windows 7 drive showing as E:

You can juggle with the letters, from the previous path. I would adise against it though, as you may end up with lost paths to running progams.
If it is of any satisfaction, when you reboot into Vista, it will again be C:

Well I've just re-installed the x86 version of the Beta - and sure enough, my C drive from Vista is my C drive in Windows 7 - none of my driver letters change in 32-bit so why should they in x64?

You've surprised me.!!
I have not yet tried to install the 32 bit Beta. Did you run it straight from the Install boot up or from within your installed OS?