Hi TMS
It depends on how the site is set up. For instance at TechIMO many forums are open to be viewed by Guests, but some forums will not allow guests to veiw posts even.
But if the forum has banned your IP address, you won't even be able to access the site from your computer as a guest, even if it is allowed. You would need another computer with a different IP address to do that.
If I were you, and you really haven't knowingly broken any rules, I'd wait for the admin's return email and sort it out.
If you are in a college campus or dormitory, and large corporate network, or some other place with a large network, it's quite possible someone else may have the same IP address.
Anyhow, feel free to make yourself welcome here while you get it sorted out.

Just check the FAQ's and you'll be fine.
Cheers
Mick