Normally you just post the raw link (or perhaps shorten it with a URL redirect).
With TwitterSplit, everything is much the same, except you put your own URL in front of any external URL, separating them with a single "?" question mark. That's it!
Format: Your link Question Mark External link
http://yourdomain.com/anydirectory/anypage.html?http://www.external.com
Once the TwitterSplit script is installed (it takes about 10 minutes) and you've prepared some simple text or a banner for the top... you're set for life. TwitterSplit auto-frames every link you post.
It's so simple even a TwitWit could do it.
A Few Notes...
Some sites (like Squidoo) over-ride TwitterSplit, but most will work perfectly. You can even add Google analytics or any other tracker if you like. You will need the ability to upload the script to your server. You can shorten the entire double URL link with any tiny URL redirect, like this example: http://is.gd/16Xm. Examples on this page include a random quote feature NOT a part of the basic TwitterSplit script.