The first video image of Osama bin Laden in nearly two years was broadcast on Al-Jazeera TV Wednesday, the eve of the second anniversary of the Sept. 11 attacks. The al-Qaida leader was shown walking through rocky terrain with his top aide, both carrying assault rifles. In an eight-minute audiotape accompanying the video footage, a speaker identified as bin Laden praises the "great damage to the enemy" on Sept. 11 and mentions five hijackers by name. On a second tape, a voice said to be that of chief deputy Ayman al-Zawahri threatens more attacks on Americans and calls on Iraqi guerrillas to "bury" U.S. troops. According to terrorism experts, such tapes reassure al-Qaida sympathizers that the terror network is still a force and its leaders still active and in seeming good health. A tape showing bin Laden would be crucial to that effort and the timing - a day before the anniversary of the Sept. 11 attacks, blamed on al-Qaida - highly symbolic.