How to add a lib to a qt project

[stampede]

You can remove the OTHER_FILES += libpg.lib, because you are going to use Qt plugin for accessing database.
You have the qsqlpsql4.dll, so you should be able to use it, try to copy this file to your applications directory, or another place where windows searches for dlls.
There is a QSqlDatabase::drivers () method, it returns a list of all available drivers.