I am trying to install a newer system on my mother's 6100. For some reason it will not install fully. I thought fine I will just boot up off of my external hard drive that I use to boot my 7100. It froze up when I did this too. I am able to boot with the exstensions off, but that is it. Does anybody have any suggestions?????

Just a suggestion, try zapping the PRAM by holding down the Command + Option + P + R immediately after you turn on the computer. Or you could backup the data from the 6100, use Drive Setup to format the hard disk and install a completely new System Folder. Try what you can until it works I guess.