ACT 1.0 and Windows server 2003

Hi all, i'm having problems with ACT 1.0 and Windows Server 2003.
Beginnig the recording of a new test, appears the login page, i write
my credentials, and when click ok closes the explorer.

Running ACT from server (with Windows server 2003 installed) works
fine, but the problem occurs when i run ACT from another machine with
Windows XP to server with Windows Server 2003.

I'm using http. In web.config, the authentication mode is set to
Windows.

Thanks for your answers.