javascript: is it possible to embed a script if it isn't already defined?

I'm having an issue where I have a page with a bunch of user interface based tabs. When a particular tab gets hit, an HTML form gets retrieved via XHR. That form has JavaScript embedded in it, some jQuery ajax form handlers, etc. Works fine and everything the first time the form is submitted. On subsequent submissions however, I get an error that looks like the following:

jQuery is not defined
[Break on this error] jQuery( function( $ ) { 

I'm not sure how this is happening, but when th开发者_如何学JAVAe form gets pulled back in, with the same exact JavaScript and jQuery handlers on subsequent submits, the error happens. Most browsers show the error, but handle it fine and the form continues to work. The wonderful IE6 however, displays an annoying dialogue box, so I need to fix this. It's as if jQuery isn't defined on subsequent submissions.

Any suggestions?

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This sounds like jQuery is actually loaded again in the HTML code you retrieve.