Hi rashley,
In true, the Value and the Caption of a submit button are usually the same thing, and as far as I had found it works ok with every browser.
Your problem, however, is a diferent thing. You want to disable the buttons, but you want the button value to be submitted anyway.
The way I would do it is by having a hidden field and then assign it the value of the pressed button, or by changing the buttons from submit to normal buttons, with a javascript handler in the onrelease that change the hidden field value and submit the form.