Download the SGS kernel flasher from the market. Only use it when dealing with Samsung ROMs (No CM!). In general, it is easier to download the .zip version of the kernels when you can, and you can then just flash them from Recovery (Choose zip). With the kernel flasher app, you can use the app to select the kernel and it can be a .tar or .zip.
Voodoo Sound is only one aspect to the app. The first lagfix was also created by the guy that writes Voodoo Sound (I think), also called voodoo lagfix. He has voodoo graphics too, for i9000 and CM, with tuned LCD patterns that supposedly take the color tinge away. I am not sure I can tell the difference on the color tinge, but the Voodoo app also has a lagfix section to control kernels that support it.
I did not think there was any lag, but I did notice a few things after converting to EXT4 that got better.