Yeah! but if you go to the post or reply screen, there is a screen asking for username and password... if there is a way for users to enter username ONLY but be able to post or reply, it 'd be great... 'cause if all users use guest username then it does not look good and no one knows who posts or replies the messages. thanks.<

I did create a username/pass as guest/guest, but what if one user change the guest password. How do I protect a user from changing this password? thanks.<

I dont know which MOD. I downloaded the version and then run it. When I clicked on this file, admin_mod_dbsetup.asp, then it seems not working. <

I've done something similar at oxle.com ; the guest account is available for guest posting. I've used the 'quickreply' box for that purpose, and created an extra field called 'nickname' which gets added to every guestpost. I've disabled login in with the guest account, so the guest account password can not be edited.
Modified files (as far as I can recall) : inc_header.asp, login.asp, post.asp, post_info.asp, topic.asp, pop_delete.asp, inc_func_common.asp.
Took me in total about 1,5 hours to mod. Feel free to dig out all info from my files ; http://www.oxle.com/source.asp (login demo/demo). <