[Lynne]

No, you need to enter is as something like /home/yourfoldername/attachments

And do NOT put it in the /forums directory. From the popup help:

If you are moving attachments into the file system, it is recommended that you do *not* place the folder under your web root (usually named public_html or www or www_root) because people will be able to bypass vBulletin's permission system and download them. Also, you will need to make the folder writeable by PHP. The easiest way to do this is CHMOD it 777 (consult your FTP, Telnet, or SSH documentation for more info on how to do this). We do not recommended that you put a folder that is CHMODed 777 under your web root - another good reason to have it located above the document root.