Sadly, your client "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.5) Gecko/20041107 Firefox/1.0" violates the automated access guidelines posted at arxiv.org, and is consequently excluded.
If you are using the PDF Plug-in, it has many bugs and is forbidden here
due to problems it causes at the server end.
You must confirm that you have disabled it before access can be restored.
(In Netscape try
Edit -> Preferences -> Navigator -> Applications,
Portable Document Format and uncheck the plug-in box.
Or delete the pdf plugin dll file from the
directory and restart browser. Or for Acroread4/Explorer5 users,
go into Acroread's
File : Preferences : General : Web_Browser_Integration
and make sure the little box is unchecked.
After a one-week grace period, access will be automatically re-enabled.)
If you believe this determination to be in error, see http://arxiv.org/denied.html for additional information.