First choose your target application. That being GW.exe. If you did it right you should see the little GW helmet icon appear.
Then tab down to "package mode".
Use the file folder icon to the right of the package window. Use this to find the mod you want to use. Your mod should appear in the window. Highlight the mod.
Then hit run. Texmod should run GW for you, that is , launch GW. If that doesn't work, try turning "post-process effects" on and off in the GW settings.