These Forums use the Live Alerts service to send e-mail. In order to change the e-mail address, you'll have to either:
1) Go to your profile in Windows Live and change your e-mail preference to send to an alternate e-mail address. However, I don't think this is possible nor have your e-mail foward to an alternate e-mail address (in Hotmail). Afaik, you can have an alternate e-mail address in live but only for the purpose of password resets, etc...
2) The other option is to create a new live account, specify your e-mail address (You can create a live account using a different smtp address) then create a new profile in Forums.
Hope this helps
Thanks.
STO Forums Test Lead