To turn on xmouse in Windows 8:

Control Panel > Ease of access > Mouse
"Activate a window by hovering over it with the mouse"

Disable auto-raise:
HKEY_CURRENT_USER\Control Panel\Desktop
The first byte of the mask controls the auto-raise behaviour, with the bit in
position 0x40. To turn it off, subtract 0x40 from the value of this byte.
e.g. if its value is 0xF1:

0xF1 = 1111 0001
0x40 = 0100 0000

F1 - 40 = 
1011 0001 = change the byte to 0xB1

Windows 8 also has a default focus delay of half a second. To turn this off,

HKEY_CURRENT_USER\Control Panel\Desktop
to 0