If the permissions have been set up to prevent changing your homepage, they have also probably been set to prevent editing the registry. If not, however, you can change this registry key to change the homepage (be careful when editing the registry, because any errors can cause serious problems):
HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main\Start Page
Alternatively, follow the instructions in this article as if you were locking the homepage, except change from "1" to "0" at step 4.
P.S. If you can, get Firefox instead of IE. It's more secure and a much better browser.