You can just copy and paste a link in, if you're having real trouble, you know! But the HTML isn't too difficult - it's just:

< a href="link">link text< /a> (without the spaces after the < )

So < a href="http://vjs2259.livejournal.com/7067.html">Here is a story about Neroon and Delenn< /a> becomes Here is a story about Neroon and Delenn.

There's a FAQ that explains the common bits of markup here, which may be useful to keep around :)