How do I back up my forum before installing Tiny Portal?

[PhilH]

When backing up my forum, will the same backup in SMF's admin panel save whatever's on the portal as well?

Yes, from TP 0.8 all TP data tables use the same prefix as SMF tables and SMF will then include those into the backup.

You can also use for example Cpanel built-in backup, to backup everything:
Cpanel --> Backup --> Generate/Download a Full Backup (Note: You cannot restore these backups, they can only be restored by your administrator)