For Sharepoint 2003, I used to check a users rights by getting the user from the SPWeb.AllUsers collection (as this contains all users of groups as well as explicitly named users, unlike SPWeb.Users). I would have then tested whether a user was in a role using something like SPRole SPWeb.Roles[“rolenametogohere”].Users.
In MOSS / WSS 3, you can instead use the following code:
public bool UserHasPermission(string username, string role, string webAbsoluteUrl)
using (SPSite siteColl = new SPSite(url))
using (SPWeb web = siteColl.OpenWeb())
SPBasePermissions requiredPerms = Web.RoleDefinitions[role].BasePermissions;
return web.DoesUserHavePermissions(username, permsMask);
Username name is string e.g. nt\robnowik
Role is Sharepoint group e.g. “Conribute”
webAbsoluteUrl is path to web you want to test users permissions against e.g. http://localhost/sites/testsite/myweb/).