If I uninstall my phpBB2 folders and install phpBB3, will the posts, members, etc. be lost?
I'm not messing around with any tables, just deleting every folder/file in my "forum" directory in my ftp.
I'm going to keep my config.php file and upload it to the new installation.
Will doing all of this mess my board up? I just don't want to lose members or posts.
you have to use the converter to convert the phpbb2 data into the phpbb3 structure, all within the same database. Either you do it on your 'live database', which means you can assign a new table prefix for phpbb3 (e.g. phpbb3_ ), so as to differentiate from the phpbb data, or you re-create a database, import the phpbb2 data (if you want to use phpbb_ prefix for phpbb3, then u have to import phpbb2 under a different table prefix) before using the converter.
then you basically install your phpbb2 forum script in another folder, in that case, your phpbb2 will never be affected, data or script wise.