Microsoft Windows 7 32bits and 64bits

Here I have a concern. I migrated my Vista 64-bit Windows 7 to 64 bits, so far it goes.

Windows 7 does not appeal to me and I wanted to go back under my vista, the concern is that the remediation system which is on my hard drive (so I have no CD) did not want to start.

By mistake, or rather out of desperation, I went back to XP 32 bit, then I went back in another version of Windows 7 but compatible 32-bit.
And now I want to go back to Windows 7 64-bit.

My setup will allow me:
Hewlett-Packard HP Pavilion p6145
6GB of RAM
2.33 GHz 4-core Processor
1TB HDD
1GB Graphqiue Card

The goal is to get the rest of the memory that is not supported by the 32-bit.

Of course, when I launch the CD in Boot Mode (Windows 7 64-bit version) it gives me nothing and on the desktop, it says it is not supported due to its 64-bit inconsistent with the 32.

Is-it's hopeless or Is there a glimmer of hope?

Your DVD Windows 7 should be linked to a license update, which requires the presence of a legal Windows already installed and activated.

It must also architecture (32 or 64 bits) is the same between OS departure and arrival. This is not the case and can not "migrate" from a Windows 32-bit to 64-bit Windows without a format the system partition.