Global Subscription Status - how to update programmatically?

Hi there,

How do I programmatically update the Global Subscription Status field on a customer card?  I have a web form that has a checkbox for the customer to (un)check for subscribing to our e-mail newsletters, and I'd like to update the Global Subscription Status field on the customer card based on the state of that checkbox.

When I click on the help link for "Global Subscription Status" field, it shows that its Field ID is globalsubscriptionstatus, and these are the possible values for it:
[LIST=1]
[*]Confirmed Opt-In
[*]Soft Opt-In
[*]Soft Opt-Out
[*]Confirmed Opt-Out
[/LIST]

So on my web form, I set the checkbox's ID and name to be globalsubscriptionstatus, then on form submit, I tried setting the checkbox's value to 0, 1 or 2, but the value on the customer card stayed the same... am I not approaching the problem correctly?