SharePoint 2007 has a new control called the SPSecurityTrimmedControl. It's a container control that allows you to hide or display a section of your page depending on whether or not the currently logged-in user has the appropriate permissions. To set the permissions, however, you need to know what SharePoint calls the permissions. Took a little while to drudge it up, but here's the list:
http://msdn2.microsoft.com/en-us/library/microsoft.sharepoint.spbasepermissions.aspx