Go to control panel User Accounts and create an account make it Admin account create password for the account then add SQL Server login for the account. Then add the account as Admin in ReportServerDB, ReportServerTempDB, and the DataSource DB. This will let you login to Report manager but your reports will not run because it will error out.
Go back to control panel then to Admin tool then local security then to local policies, then User Rights Assignment scroll down to Allow Logon locally double click it and then Add that account to the list of accounts. This will let you see the Reports but login is still required.
Now the last step to remove the login prompt open IE go to tools options and then security then click local intranet, then sites then click Automatically detect intranet network, then Advanced and then add the Report Manager url in there and the login prompt will go away. I had to do this because I tried the option posted by SSRS employee and my SSRS config file did not include what the person said to remove. I run VS2008 Team Suites which is he Team Foundation Server Main Development Tool. So print out the above and get to work and Goodluck.