Recently, I have found out that embedding videos without plugins can be done easily in wordpress. Not only it works with YouTube and Vimeos, I have tested, it worked with older version of WP, even with 2.9 version!
Add SWF to WordPress — Embed Flash
How to embed flash files or code and How to add SWF to wordpress.
WordPress Add Video To Post
Want to add YouTube video (or others) to your wordpress post without plugin? I will show you how i did it without extra plugin.