How to downgrade Windows 7 Ultimate to Windows Vista without losing any data

[DeckardShaw]

I wanted to upgrade my BIOS to the latest version because I am upgrading my Intel core 2 duo T5250 1.5 GHz to the Intel core 2 duo T9300 2.5 GHz .The latest version of the BIOS added support of the T9300 to the Pavilion dv6500. I researched on the net and found out that I could only flash the BIOS on the original version of Windows with which the laptop came that is Windows Vista . Could you suggest me a method through which I could downgrade my Windows 7 Ultimate to Windows Vista while keeping  all of my files and data simultaneously.

Chipset : Intel GM965 Express Chipset

BIOS : Version F.22 

Folders and data are distributed in three disk  partitions : LOCAL DISKS : C,D and E 

Total HDD space : 500 GB out of which around 250 GB is used.

[WAWood]

@DeckardShaw 

Sorry, but while MS does often offer an Upgrade Path from one OS version to the next -- an Upgrade in which the settings, data, and apps are retained -- there is simply no Downrade equivalent.

The only way to so this is a clean install of the older OS version and that retains nothing.