I don't know if i am understanding this correctly but in your phpMyAdmin just delete the tables you don't want and then do an import
of the old tables you want or instead of an import you can run a sql
For instance i want to use my old mytrb_forums so i would delete the new mytrb_forums table and do a an import using my old backup
or just Run SQL
Somthing like this :
CREATE TABLE IF NOT EXISTS `mytrb_forums` (
`fid` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(120) NOT NULL DEFAULT '',
`description` text NOT NULL,
`linkto` varchar(180) NOT NULL DEFAULT '',
`type` char(1) NOT NULL DEFAULT '',
`pid` smallint(5) unsigned NOT NULL DEFAULT '0',
`parentlist` text NOT NULL,
`disporder` smallint(5) unsigned NOT NULL DEFAULT '0',
`active` tinyint(1) NOT NULL DEFAULT '0',
`open` tinyint(1) NOT NULL DEFAULT '0',
`threads` int(10) unsigned NOT NULL DEFAULT '0',
`posts` int(10) unsigned NOT NULL DEFAULT '0',
`lastpost` int(10) unsigned NOT NULL DEFAULT '0',
`lastposter` varchar(120) NOT NULL DEFAULT '',
`lastposteruid` int(10) unsigned NOT NULL DEFAULT '0',
`lastposttid` int(10) unsigned NOT NULL DEFAULT '0',
`lastpostsubject` varchar(120) NOT NULL DEFAULT '',
`allowhtml` tinyint(1) NOT NULL DEFAULT '0',
`allowmycode` tinyint(1) NOT NULL DEFAULT '0',
`allowsmilies` tinyint(1) NOT NULL DEFAULT '0',
`allowimgcode` tinyint(1) NOT NULL DEFAULT '0',
`allowvideocode` tinyint(1) NOT NULL DEFAULT '0',
`allowpicons` tinyint(1) NOT NULL DEFAULT '0',
`allowtratings` tinyint(1) NOT NULL DEFAULT '0',
`usepostcounts` tinyint(1) NOT NULL DEFAULT '0',
`usethreadcounts` tinyint(1) NOT NULL DEFAULT '0',
`requireprefix` tinyint(1) NOT NULL DEFAULT '0',
`password` varchar(50) NOT NULL DEFAULT '',
`showinjump` tinyint(1) NOT NULL DEFAULT '0',
`style` smallint(5) unsigned NOT NULL DEFAULT '0',
`overridestyle` tinyint(1) NOT NULL DEFAULT '0',
`rulestype` tinyint(1) NOT NULL DEFAULT '0',
`rulestitle` varchar(200) NOT NULL DEFAULT '',
`rules` text NOT NULL,
`unapprovedthreads` int(10) unsigned NOT NULL DEFAULT '0',
`unapprovedposts` int(10) unsigned NOT NULL DEFAULT '0',
`deletedthreads` int(10) unsigned NOT NULL DEFAULT '0',
`deletedposts` int(10) unsigned NOT NULL DEFAULT '0',
`defaultdatecut` smallint(4) unsigned NOT NULL DEFAULT '0',
`defaultsortby` varchar(10) NOT NULL DEFAULT '',
`defaultsortorder` varchar(4) NOT NULL DEFAULT '',
PRIMARY KEY (`fid`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=28 ;
--
-- Dumping data for table `mytrb_forums`
--
INSERT INTO `mytrb_forums` (`fid`, `name`, `description`, `linkto`, `type`, `pid`, `parentlist`, `disporder`, `active`, `open`, `threads`, `posts`, `lastpost`, `lastposter`, `lastposteruid`, `lastposttid`, `lastpostsubject`, `allowhtml`, `allowmycode`, `allowsmilies`, `allowimgcode`, `allowvideocode`, `allowpicons`, `allowtratings`, `usepostcounts`, `usethreadcounts`, `requireprefix`, `password`, `showinjump`, `style`, `overridestyle`, `rulestype`, `rulestitle`, `rules`, `unapprovedthreads`, `unapprovedposts`, `deletedthreads`, `deletedposts`, `defaultdatecut`, `defaultsortby`, `defaultsortorder`) VALUES
(1, 'Welcome To The Support Forums', '', '', 'c', 0, '1', 1, 1, 0, 0, 0, 0, '0', 0, 0, '', 0, 1, 1, 1, 1, 1, 1, 1, 1, 0, '', 1, 0, 0, 0, '', '', 0, 0, 0, 0, 0, '', ''),
(2, 'Member Introductions', 'New here? Come in and introduce yourself to the fellow members of the forum.', '', 'f', 1, '1,2', 1, 1, 1, 0, 0, 0, '0', 0, 0, '', 0, 1, 1, 1, 1, 1, 1, 1, 1, 0, '', 1, 0, 0, 0, '', '', 0, 0, 0, 0, 0, '', ''),