is it possible to modify the applications that are on the dock on the touchwiz ?

Switch to Launcher Pro. You won't regret it! :-)

I know launcher pro is better i even got the launcher pro plus, but i wondered if its possible to use the touch wiz and modify the dock

yes it is possible to change the shortcuts on touchwiz. open the applications menu, press the menu button, then edit. now you can drag any of the apps in your menu onto the dock bar. you cant replace the home on the dock bar though.