Create an Installer for Windows Software

I have the need for the creation of a Windows Installer. Project is VERY simple. Installer should be developed in Open Source or Free Installer Language. (NSIS or WIX Preferred.) Install shall be fully customized with custom splash screens (I will ask for your exact sizes for my graphic artist to create.) It needs to display a License Agreement, Copy a number of files to the (x86) Program Files Directory. It will then ask the end user a selection process and based upon their answer will update an XML file and if necessary kick off additional scripts based upon the user selection. Program should also be able to update existing application if it exists for application updating. This will include updating XML file and binaries. Application is written in .Net 4.5 and is ready for packaging today!