After you defeat Andariel in the Diablo II beta, you can talk to Warriv the caravan master, who in the final game will take you east through the Monastery pass to Lut Gholein, the city where Act II is centered. In the beta, however, when you ask Warriv to take you east, you get a slideshow of screenshots showing off the later acts, including a screenshot of Act IV and a great portal that leads to some unknown confrontation. The rest of the screens show off the desert locale and underground dungeons of Act II and the jungle terrain of Act III. You can view the screenshots by clicking above.