Search google, ppc, or xda for g-sensor mods. There are also some registry tweaks which can be found here:
http://forum.ppcgeeks.com/showthread.php?t=110249
Enable TF3D AutoRotate/Diable, delete these keys
[HKEY_CURRENT_USER\Software\HTC\Manila]
"EnableLandscape"="true"
[HKEY_CURRENT_USER\Software\HTC\HTCSENSOR\GSensor\M oduleName]
"TF3D"="\Windows\manila.exe"
[HKEY_CURRENT_USER\Software\HTC\HTCSENSOR\GSensor\W hiteList]
"TF3D"="Manila"