I was given the task of writing some code to add a user or group to a role on a SQL 2005 Express Edition Reporting Services server.
The natural answer to the problem of giving users access to a Reporting Services server is to create your own roles for which only the required Tasks are allowed.
Creating roles is not allowed as it is a limitation of Express Edition. So – your best bet is to find the most suitable predefined role to assign your user / group to.
The single biggest issue I found in trying to do this was identifying the predefined roles.