FFS GW, use your head! I don't have GIMP yet I've used that tutorial. They are very similar programs, it's not hard to work out what you're meant to do.
*decides to be very nice*
Edge-detect isn't a PS filter. Instead, try using poster-edges. Or experiment until you find an effect that makes them look like EA.
Colorize is instead found here: Image > Adjustments > Hue/Saturation
Brightness/Contrast is also found in the Adjustments menu.
So one missing filter and two things under a different menu.
Edited by mh_gollum, 05 February 2008 - 02:32 PM.