How to do an automated installation of Ubuntu on 100 Remote machines?

under debian/ubuntu its called preseeding: https://help.ubuntu.com/9.10/installation-guide/powerpc/preseed-using.html

You can put the preseed.cfg on CD oder let it load via web. I`m using it in conjunction with cfengine2

I would recommend looking into Cobbler to see if it can work for you. It was primarily developed for RedHat based systems, but it looks like Ubuntu may be usable. Considering that Cobbler supports both PXE as well as boot discs, it should be able to scale to your needs.

You could try using FAI (Fully Automatic Installation): http://www.informatik.uni-koeln.de/fai/features/