are you double clicking the mxp file to start the install?
if so try starting the install manually:
In Dreamweaver, go to Commands -> Manage Extensions to open the extesnion manager.
Once the extesnion manager is open, close Dreamweaver.
In the extesnion manager, click the install New extesnion icon. In the Finder Window, browse to the MXP File you downloaded and select it to begin the installation.
Button styler will only work with Form button elements.
to change the text from submit to something elese, edit the buttons Value attribute, for example the code for a submit button may look like this:
<input type="submit" name="btnSubmit" id="btnSubmit" value="Submit" alt="Submit" />
changing the value:
value="Submit"
will change the text shown in the browser.