Single post redirect by post_ID without plugin

I am running two WPs. Old one (2.5) and new one (3.0.3). The new one is a exact copy of the old one but the post IDs are different. I need to redirect any requests to old post_IDs to the new post_IDs of the new (3.0.3.)WP. Without plugin! so I can delete the (2.5) version (running on the old PHP4) forever.

…so for example why the .htaccess redirect would not work?

redirect 301 /old_wordpress_blog/?p=123 http://www.mysite/new_wordpress_blog/?p=987

or

redirect 301 “/old_wordpress_blog/?p=123” http://www.mysite/new_wordpress_blog/?p=987

The idea would be to manage the incoming referrers who are still linking to the old post IDs so they are seamlessly redirected.

Thank you for any good help!