Hi, to get this to work you'll first need to
install a DX8 to DX9 convertor. Get it here
http://enbdev.com/convertor_dx8_dx9_v0035.htm
Put downloaded files in the main folder.
Then just add SweetFX to the Main Folder
of Sin Gold.
UPDATE 2016/02/23
If you are using Reshade selecting DirectX 8 in Preset settings gives the same result as using a converter. The same goes for SweetFX 2.0; just renaming Reshade32.dll to d3d8. No need for a converter anymore.