If you decide to go with Unity it's relatively easy to setup most of the coding. Here's an example project http://unity3d.com/support/resources/tutorials/2d-gameplay-tutorial
Here is a tutorial specifically for Side-Scrolling: http://widff.co.uk/DevBlog/?p=777 If you ever run into any issues, deferentially go on UDN like Bal said. Lots of documentation can be found there for almost any issue you run across into.