See, I saw this question and I was like Yeah, how do you do that? So I decided to do some researching. And I found a way to do this - I don't know if it's the only way or the best way.

Edit your theme. When you do that, add a module on - the one called "Xanga TV". (You don't have to save this or anything.) Ah, but you don't want the module, you want it embedded in a post, eh? Well, I figured that out.
There's a button that says "embed" on the bar (chat, questions, highlights). Click that and copy the code. Now you can get out of editing - you don't have to save unless you want the Xanga TV module.
Okay, so we have the code. Now post a new entry. In this entry, just paste the code that you copied. Voila!! (Since it's all HTML stuff, you might have to click "insert HTML" when you post the entry - on the top right. I have to on my computer to make it work or else it's just a bunch of codes.)

Good luck!! :D