Not counting the OEM variants, what was officially released by Microsoft in the Windows Vista editions range for business and individual consumers were:

Starter - 32 bit only
Home Basic - 32 bit edition and 62 bit edition
Home Premium - 32 bit edition and 62 bit edition
Business - 32 bit edition and 62 bit edition
Enterprise - 32 bit edition and 62 bit edition
Ultimate - 32 bit edition and 62 bit edition
Business for embedded systems -
Ultimate for embedded systems -
Home Basic N - 32 bit edition and 62 bit edition
Home Basic K - 32 bit edition and 62 bit edition
Home Basic KN - 32 bit edition and 62 bit edition

Then you have the various specialised OEM versions.

With most of the Windows Vista systems you have do a clean install over the others if you want to change them.

Most of the software designed for other versions of Windows are not compatible with Windows Vista, or the reverse.

...........

Most packages and applications for one version of Linux will work on another, and I've had a lot of success in the past in installing one version of Linux over another while still carrying across a lot of personalised settings and data due to having the 'Home' directory in a separate partition.