[falko]

I'd make a backup of all important files before you install ISPConfig. You could also make an image of your current installation before you install ISPconfig. There's a howto aboout this: http://www.howtoforge.com/howto_linux_systemimager

Then, after you'e unpacked ISPConfig and before you run

./setup

, have a look at dist.txt and the files in the mod directory. As you have a non-standard Apache installation, you might have to adjust these files a little bit.