If you are writing a module for DotNetNuke that depends on jQuery, you must find a reliable way to make sure jQuery is loaded. Furthermore, you must make sure the right version of jQuery is loaded and must also ensure the rest of the DNN installation is not affected. Here is how you can do that.
1. Detect whether jQuery is installed
2. Determine whether the right version of jQuery is installed. I will use 1.4.2 as my base.
3. Make sure to not cause conflict with other libraries that might be using the $ variable
Will Strohl has put together a great article on the best practices for using jQuery within DNN