The only obvious problem I see is that you're not calling
the .splitter() plugin anywhere. Also you are missing the basic css
required to show the splitbar etc.; see the sample pages and get it
from there.
I would load splitter.js through a normal script tag on the page,
there's no reason to wait until the ajax content arrives.
Then your ajax call would look like this:
$.ajax({
type: "GET",
url: "content.php",
success: function(content){
$("Container").html(content);
$("MySplitter").splitter(type:'h');
}
});