Having tested the WPI version multiple times, it's easier to set up SQL and manually install DNN. Especially with DNN7 that asks you very little. I've found that the guaranteed way to always have it work is to create a database in advance, use a SQL login (SA works fine) and configure that manually in the DNN setup. Other than that, assigning IIS permissions is the only other issue, create the IIS site with a new app pool and use the IIS AppPool name for MODIFY permission in the DNN folders. Set the app pool for 4.x and you're usually good to go.

Jeff