So, after a lot of investigation i could find out the following:
GnomeWoW is working like charme! If there are problems with captcha, realminfo or mail, then it's perhaps a problem with the php installation. I had only trouble after switching to the official php 5.3.8 32-Bit release at windows.
If you're using Windows 64-Bit, then i would recommend the following products:
Apache 2.2.1 64-Bit from apachelounge.com ( http://www.apachelounge.com/download/win64/ )
PHP 5.3.5 64-Bit (VC-9 Threadsafe) from Anindya's Blog ( http://www.anindya.com/php-5-3-5-x64-64-bit-for-windows/ )
Follow the correspondending installation manuals (it's really easy, perhaps i'll write a how-to later)
With this bundle GnomePHP/WoW should work as it should without any problems.