hi i want to know how can i bound some some to register on forum if he want to downlaod anything by clicking on any link any idea
Admin > Members > Permissions > General Permissions
After Guests there is modify-link
View attachments remove tab and save.
I don't know of any mods that display the link but prompt guests to login. You're currently limited with 2.0 and available mods.
But you can try a download system:
http://custom.simplemachines.org/mods/index.php?mod=992