It should work. gunni gave the links to get MADDE and QtCreator tied together. Be aware that PR1.1 firmware only has Qt4.5 as the baseline, so I've only used the v4.5 SDK (plus MADDE current is Qt4.5).

I don't care/worry too much about the runtime device debugger section just yet. Most of the things I'm doing are manual labor... eg I use QtCreator for development and and to test the application UI locally on the desktop to make sure there are no broken code blocks. Then I use MADDE to do the n900 device build for me and copy the executable over.

MADDE is the only cross-platform toolchain you'll need to build complete n900 applications (easiest install method I know of). Don't concern yourself about the particular core, as that only affects you if you're using some device specific code like hardware access, kernel access, etc. But if you're only mostly doing user applications, then using Qt and standard Linux libs are all you need to know.

Qt is meant to be virtually write-once, compile anywhere SDK; it's that flexible, although with some caveats. So your single HelloWorld source code can be compiled for any platform supported by Qt (windows, linux, maemo, osx); it all depends on your output target.

I can't speak more from an expert p.o.v because like you, I'm just starting to delve into maemo+Qt and I was a little daunted with simply getting started. But once I got MADDE installed and QtCreator there, it made it a lot more obvious.

My first attempt is a project I'm hosting on google (http://code.google.com/p/maemocalllogviewer/) which is a call log viewer which displays a bit more information that the standard N900 call log. You can grab the source code from there and compile for yourself (using my example of going into MADDE, and doing "mad qmake MaemoCallLogViewer.pro" and "mad make"). I've also uploaded a compiled binary on the project site.