Il concetto:

<form>
<input type="button" name="start_01" onclick="this.disabled=true;this.form.stop_01.disa bled=false">
<input type="button" name="stop_01" onclick="this.disabled=true;this.form.start_01.dis abled=false" disabled>
<hr>
<input type="button" name="start_02" onclick="this.disabled=true;this.form.stop_02.disa bled=false">
<input type="button" name="stop_02" onclick="this.disabled=true;this.form.start_02.dis abled=false" disabled>
</form>

ciao