Dual boot Overwrite

Maybe you guys can tell me what to expect before i screw my system up. I have 2 drives installed in my desktop one is an 80gb drive with windows 7 32bit installed on it, this one i use for my every day use.
I also have a 250Gb drive with Vista 64 home premium. The Vista install was my everyday drive untill i got W7U32b when i got W7U32b i bought the 80gb drive specifically to install the W7U32b to so i wouldnt loose what i had on my vista drive,,, needless to say ive never even gone back to use the vista drive since then except to copy files over to the W7U32b drive .
I want to now install W7U 64 bit over the vista drive. Right now when my system boots i have the option of starting in win 7 and or vista. If install w7u64 over the vista install will i then have the option to boot in either w7u32b or w7u64 bit? i DO NOT want to loose the W7U32b drive data!!!
Ive done some searching around but didnt find anything similar to this. Any info would be much appreciated!!
Thanks
JRockZ

To answer your question specifically, I'm not sure how windows boot manager works for same versions of windows. In the past, you install the older os followed by the new one. In this case it's the same. But, someone will come by with a detailed answer soon i'm sure.

In the meantime, have you considered formating the vista drive, and using it to host a virtual machine from? I suspect you want to play around with application compatibility, driver support, etc. and virtual machines make it so convenient.

Thanks guys, to anser "Bare Foot Kid" heres a clip of my drives layout
C: Drive Windows 7 Ultimate 32 Bit
D: Vista Home Premium 64bit

Bare Foot Kid Thanks thats exactly what i thought you would say Hahahaaa! The start up repairs part is what scares me but i'll get it!! will report back when i get around to doing it and let ya know how it went.
Thanks
JRockZ

Have you now confirmed that the one-time BIOS Boot menu works to boot the OS HD not set to boot first in BIOS setup?

If so when you install Win7 64 bit on DISK1 unplug DISK0 so that the installer doesn't configure a Windows-managed Dual Boot with Win7 32 bit which would place the System boot files on DISK0.

Be sure to set DISK1 as first HD to boot in BIOS setup.

After 64 bit install, plug back in DISK0, set preferred OS HD as first to boot in BIOS setup, boot the other OS HD using the one-time BIOS Boot Menu key. This keeps the HD's independent to come and go as you please.

If you have a rare mobo which doesn't have the one-time BIOS Boot Menu key, or prefer not to Dual Boot using the BIOS, then keep DISK0 plugged in when you install Win7 64 bit to DISK1 so it configures a Windows-managed Dual Boot.

Hey All,, rathe rthan unplugging my sata drives and dealing with a big mess inside my pc i just went into my vista install and did an in place upgrade worked perfect and been using it a week or two now, i did have to go in and BCD edit so that i could name my two installs one as 32 bit and the other as 64 bit.
Thanks for all the help.
JRockZ

Since you already have a WIndows-managed Dual Boot and apparently don't want to change that, you can also clean install Win7 directly to DISK1 if you have any issues with the in-place Upgrade from Vista. Clean Install Windows 7

Sometimes an in-place Upgrade can suffer from importing corrupt settings from Vista. I wouldn't settle for less than instantaneous performance.

Win7 installer will configure the Dual Boot menu with the other Win7.