I'm not familiar with Joomla. You embed our form in any webiste using an embed code - you can get it by going to the Distribute tab and selecting Embed.
Once you have the code you could ask the Joomla folks on their forum on how to embed it. If you find the answer please repost here so others will know how to do it.
I just did this on a site of ours. In my case it was a matter of clicking the "Source" button in the WYSIWYG editor and pasting it in there. Keep in mind however that the default install of Joomla typically blacklists certain HTML element tags (Global Config -> Text Filters in 2.5.7) so you may have to adjust this before it will accept SCRIPT tags.