In the next few days I will (hardware)upgrade my system from a 'stoneage' 32-bit motherboard and CPU to a modern 64-bit with an AMD X2-processor.
I have an empty harddisk available and want to install, via netinst-amd64, the completely - as far as available - 64-bit version of LENNY.
My nowadays installation contains some 72k of files and directories, with perfect functionality, all maintained via aptitude.
Via netinst I want to get on the new disk exactly the same applications, that I now have, not more and not less.
Writing down the *aptitude-contents now* from "installed" and then selecting these under the new installation is a task, that a medieval monk would have done, but not me:-)
Is there a way to copy (via a helpful Knoppix-CD if necessary) all the wanted applications automagically into aptitude and let the program then do the upgrade?
Anyway, I don't want my nowadays other disks to be overwritten with the new system; I need all the configurations and other things on them *till* I have the new system up-and-running to my full satisfaction.

You'll need to look at the aptitude man-pages and in particular the --get-selections and --set-selections options

I think you mean dpkg because I just looked at the aptitude man page and the options are not in my copy of it. For the OP to use this method on your now existing install dpkg --get-selections > selections.txt then copy the selections.txt to the new install after having just done a base install (eg. unselect the extra packages like the desktop task when doing the netinstall when you get to this part of the install) then use dpkg --set-selections < selections.txt when logged in as root at the console. Now you would use dselect update then apt-get dselect-upgrade to install the list you just set. If wanting to use aptitude for your package installer from this point on then I believe you would use aptitude keep-all to set the packages installed on your system then you can continue as normal using aptitude.

Errr, you're right. It should be dpkg instead of aptitude...

Sorry, I don't want to be impolite by not answering, but the new hardware hasn't arrived yet. So please have a little patience, I will then report my woes and wees.
Thanks already now for your profound instructions.

Well I made it a long quote just to point out, that the described method worked like a charm from beginning to end!
Only one minor glitch occurred: I had to install also the lib32 to get *all* my old programs working.

Thank you very much.