Hello, what Redhat version is practical to install on a 150 MHz laptop with 80 Mbyte RAM ? I want to be able to use virtual desktops.

I've noticed latest versions aren't really suited because they assume the existance of much more computational and memory resources that really makes things go slow.

Approximately at what Redhat version did a 150 MHz laptop with 80 Mbyte RAM become a problem ?

Well I've been trying to find a usable distro for my Toshiba Libretto ct70 (133 Mhz, 32Mb ram) for some time, as it has a crazy pcmcia floppy and no on board cdrom drive it has been quite a problem. I have installed RH5 from a parallel port cdrom, but have found upgrading the supplied packages very difficult, with almost endles dependancy problems. However I recently tried Damn Small Linux, which is alinux live cd version with lightweight applications.(perfect for older hardware) On their website are instructions for copying the files to your hard drive and it all works well, ok perhaps a little slowly, but its the best I've found so far. It can be found here:
www.damnsmalllinux.org Best of Luck.

Consider a different distro than RH for that hardware. Slackware is a lighter distro. As is Debian. They will run more smoothly on that hardware. They may not be as easy to use, but they are not as hard as they are cracked up to be. I found the Slackware installation to be pretty painless. I had mentally prepared myself for a couple hours of hell the first time I installed it. Turned out to be fairly simple.