XP Pro is no longer the license offered for OS my Microsoft, of course you can still find systems that are last in stock with OEM licenses of XP, or even Retail packages. However any license sold on Volume Licensing Programs are Vista and then you can use a free downgrade by installing the right Media DVD
Vista Ultimate 32 this license “32 bits” is as Vista Business but includes Media Center, Bitlocker Drive Encryption (encryption of data). Is free if you have Windows with SA, and it will require a separate key and media available for free on the MVLS or eOpen site, available to volume licensing clients.
Vista Business 32 “32 bits” edition of Vista. Normally licenses with 3GB of memory.
Vista Business 64 “64 bit” edition of Vista. Normally for computers with 4GB memory or higher with a greater demand to have multiple applications opened at the same time. If you want to check if your systems are compatible with this edition please check http://www.microsoft.com/windows/compatibility/