Enbedding AD in article with JS

[Allen4172]

I'm new to JS and not really sure where to start with this. Basically I'm trying to enbed an ad inside article content without manually having to do it. My goal is to get something similar to how www.sportsline.com does theirs.

My idea would be to have something like this:

[code]
<script>
---some code here---
</script>
Some article content
[/code]

The script would then go to the end of the first paragraph and then insert the ad. Any ideas or suggestions?