If you had read any of the results that google returned, you would have found this:
Quote: "Instructions to active directx 10.1 on Windows vista:
1) Save
this text file as File.cmd
2) Then run the batch file with elevated administrator privileges.
3) Install and reboot the computer after installing each update: KB935509, KB937287 and KB93837.
4) After the final reboot, you will get the option to download Windows Vista SP1 in Windows Update.
5) Verify that you have DirectX 10.1 by running dxdiag from the command prompt."
This signature is legen-wait for it... dary };]