IB provide sample Apps in C, VB and Java. I choose to use the Java platform for independance and stability.
As it happens I am considering making my trading App (very basic, one click market orders only with built in simulation of off the live feed) and Historical Data Downloader available.
The hardest part of this app would be the user interface IMHO, generating the orders is a doddle. Of course MrX didn't mention how he manages positions etc etc which could make the app complex.
Of course I would help out on specific questions but IB do also have a good API forum.
JonnyT