How to get AHCI support on an IDE Windows 7 installation? [duplicate]

You don't have to reinstall Windows to enable AHCI. From this Microsoft Support article:

1. Exit all Windows-based programs.
2. Click Start, type regedit in the Start Search box, and then press Enter.
   If you receive the User Account Control dialog box, click Continue.
3. Locate and then click one of the following registry subkeys:
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Msahci HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\IastorV
4. In the pane on the right side, right-click Start in the Name column, and then click Modify.
   In the Value data box, type 0, and then click OK.
   On the File menu, click Exit to close Registry Editor.

Caution is necessary when mucking around in the registry. If you're uncomfortable with doing it yourself, Microsoft also offers an automated "Fix-It" utility to do it for you.