The easiest way would be to change the Welcome Dialog box to have the warnings and what not that you want the user to read.
I will assume you are using Wise for Windows Installer 3.x. Goto Setup Editor and click on Welcome Dialog, In the right hand pane simply double click any existing text to add more text to it. Or right click the Welcome dialog, select Add from the popup window, then select Text. Wack in your text set where in the dialog box you want it to appear, x and y pos. Re-Compile the msi and away you go.
If your users are similar to mine then they more than likely wont read it anyway. But hey what can you do.
Silly question, but why are you using scriptit. I have had nothing but trouble with it. Is there no other way to automate what you are doing by using a vbscript or response file?
Clint