The QNetworkAccessManager and associated classes are for very low-level processing. We use that stuff for talking directly with web services, email servers, and the like.
You should use something higher level. Take a look at the dockWelcome script in the xtdesktop extension instead. It's about 120 lines that I'll summarize here.
initWelcome() sets up that particular page of the desktop. The associated UI has 3 buttons for basic web navigation.
initWelcome() is called as the desktop client is starting up and does the following:
If you don't need the buttons, the URL is simple, and you're working with just one version of the xTuple desktop client, this can be done in 10-15 lines of code.