there are a few ways I can think of (I haven't tried them though, so you may need to experiment a bit.)
a) on the form properties, advanced tab, set the form to use a different generic header (one without a menu.) This approach is the simplest, but does mean tweaking the setting for all forms.
b) alternatively, a "global" approach, is to embed some code in WebHandler, in the MakePage method. The second parameter there contains the procedure type, in this case you'd be checking for Net:Web:Form
So, you could, for example do something like (BEFORE the parent call);
if p_Type = net:Web:Form
p_web.SetValue('IsAForm',1)
end
Then set the menu condition to
p_web.GetValue('IsAForm') <> 1
cheers
Bruce