Whether or not to use the undergravel filter is dependant on what you plan on doing with your tank. If you plan on doing gravel with artificial plants, it will help keep your gravel clean. However, if you're using sand or another fine substrate, or if you plan on doing live plants in the substrate, you'll want to remove it. I have a couple of tanks that I do use the undergravel filter in, and it does an amazing job of keeping the gravel clean (I also use a HOB filter for those tanks).
Let us know if you plan on using it, if so I'm sure we can help you find the resources to get it set up.
