1./ Install Khmer Os System (you can download it from Khmeros.info
2. Save the following into fixvista.reg, then double click to install it. 

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Fonts]
"Daunpenh (TrueType)"=-
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\FontSubstitutes]
"DaunPenh"="Khmer OS System"