Restoring SQL database with a different prefix

I hope some MySQL guru can help me here.

I was previously running WP 1.2, and decided to upgrade to 1.5. I had an SQL database where the tables had the prefix “wp_” — I saved this database to an *.sql file to back it up.

The upgrade didn’t go well, I got frustrated, and eventually did a clean install. I tried to use the old database, but lo and behold, WP wouldn’t permit it, saying “it appears you’ve already installed WordPress.” So in my root/wp/wp-config.php file, I set the following variable:
$table_prefix = ‘wp2_’;

This gave me a fresh installation of WordPress, using the same SQL database as before, but with two sets of tables, wp_table and wp2_table.

Now what I want to do is to import my backed-up SQL file so as to recover my old posts and comments. If I do a standard backup [codex.wordpress.org], then the information simply returns to the old tables with the “wp_” prefix, which isn’t being read by my new installation of WP 1.5.

My question, I suppose, is this: is there a way to conduct the reimportation of database information, but to alter the prefixes in the process? I’d like to put the “wp_” information into the newer “wp2_” tables. My follow-up question is, since these tables have all sorts of information other than just post and comment content, is doing this going to totally ruin my new installation? Are my old posts gone forever?