ad_form has a '-has_submit' flag that allows you to suppress the ad_form generated submit button and then you can supply your own. The confusing thing (to me) is that '-has_submit 1' means the submit button is not generated for you. In any case, here's a snippet that would do what you want:
ad_form -name test -form {
field1:text
{my_submit_button:text(submit) {label "Click me"} {html {onClick "Disab"}}}
} -has_submit 1
...