If you purchased the retail copy, you can convert your trial by navigating to SharePoint 3.0 Central Administration.
- Log on to Windows SharePoint Services server -> On the Windows Start menu -> click Microsoft Office Server -> All Programs menu -> SharePoint 3.0 Central Administration
If you know the URL, access the Central Administration page remotely, access the site admin page by entering the URL on IE browser.
- Click on Operations tab
- Click on Convert License Type under Upgrade and Migration
- Enter Product Key to activate the product