OK. I backup all the sub-folders under each mailbox, including the top of information store, w/no problem. Currently running Backup Exec v10d, Windows 2000, Exchange 2000. I didn't recall that folder being there, but I have only had to restore messages or mailboxes a handful of times over the past 3+ years, outside of semi-annual testing. I just select the mailbox level and everything under it. I'm looking forward to moving from v10 -> v12 this summer so that I can eliminate the slow brick level backups, but still have the ability to restore individual messages.
You might check out the following web site -
http://www.backupexecfaq.com/. It seems to be kept up to date.
John