ChooseColor isn't a function, it doesn't exist. If you go to the link TheSteve has posted you see a list of functions, which are called Windows API functions (for user32.dll).
PS, for running a file (no matter what kind), you can also use:
code:
new ActiveXObject("WScript.Shell").Run("\"C:\\path to file\\file.bat\"");
which is way shorter than using ShellExecute.