Choice of Distributive

I throw out my last desktop at 1994, and since 1995 used laptops only. Some I sold out, some of them I keep, in spite of I alredy bought the new model of hsrdware. In first turn, these was Toshiba Portege laptops. I very high value that You can leave station at home with CD-ROM, floppy drive and all perifereal devices, as printer, plotter , internet router and so on. At 2007 i find, that at my home there are few old Toshiba laptops, the latest of them was portege M100, and others was Toshiba Portege 2200 and 7200.
I extend RAM at M100 up to max. 2GB and 2200 and 7200 to 128 and 320 MB respectively. So, I find, that if 7200 slightly low for using 3-d AutoCAD, but possible to work, just need to minimize number of packages running and some scetch elements dissapeared if scetch rotating, bbut after rotation stopped, they are take their own place. And M100, especially after Ram uprading, really fly and no scetch fragments dissapeared, when rotation. So, I decide not buy new 2-kernel notebooks, because of valuable price. And because of last time I works on a big UNIX mashines, I remember, that Linux works faster on weak mashines and think about of using Portege 7200 and even 2200 to create scetches, if I can find CAD packages for Linux. So, I try to find at first distributive, which I will use, and after internet serfing I decide, that Debian - is my choice. I immediately download small distr and unsaccesful tryed to install it on my flashcard, then on to RW-CDROM.
Flash-card installation I don't study up to this time.
And as to install to CDROM zip file with kernel, at first was unsuccessful, so I go to the marcket, and seller advice me to get a KNOPPIX as for beginner. I read, that KNOPPIX can be used as Live CD distr, and decided, that I can use it for to knowing what is it - Linux?
When I install Knoppix on Toshiba Portege 7200, I check, that there are option - install like Debian system, and exited, but this time I continued Live CD installation first.