Role Assignment without using Report Manager

Hello,
I'm having some problems using the Report Manager, but I *really* need
to make a role assignment now. Can't wait to have the problem with
Report Manager solved.
So, I would like to make this role assignment directly in the
ReportServer database, using the SP SetPolicy or some other SP.
I'm looking for the equivalent of making the "New Role Assignment" and
then
Group or user name: Everyone
Role "Browser" checked
OK
Can anyone tell me exactly how to do this?
Thanks in advance,
Filipe Henriques
PS: By the way, the problem I've got using the Report Manager is that
always appear "The request failed with HTTP status 404: Not Found.",
although I can see perfectly the Report Server page.
Does anyone knows what's the problem?Ok, I found this link:
http://blogs.msdn.com/bryanke/archive/2004/03/17/91736.aspx
for "Sample Script for Setting Item-level Security in Reporting Services".
It's all I need.