I couldn't make it throught this whole thread -- read 5 pages and just skipped to the end here (so far).
I'm going to be the odd man out here again, and totally confuse the "which flavor should I use" question. But the simple truth is:
I use Puppy Linux. And have for years.
I can and do occasionally dual boot into XP or Win7 or whatever windizzy hyper slowness is on the boot sector of whatever computer I'm using to do occasional jobs with oddball windizzy software that won't work in WINE in Linux.
BUT, 99% of the time it's this amazing free OS that is about 100 megabytes in size TOTAL, WITH APPLICATIONS that run IN MEMORY at about ten times the speed of windizzy programs, CAN RUN off a CD, with NO installation necessary, and will EVEN RUN on a 486 machine, DOESN'T require antivirus software, and DOESN'T crash, and DOESN'T waste my time automatically updating itself, or try to force my computer to close, or tell me to wait to shut it off, or wait to start using it, or try to record what I'm doing, or try to sell me software, or install crippled "freeware", or try to hide it's inner workings.
I get enough of those problems when I occasionally boot back int Win 7.
And if you liked Win98 (I did) Puppy Linux will look real familiar, unless you want to trick it out. I don't, but you can.
If you want to run Puppy Linux, just download a copy onto a CD and run it from there. No need to install.
If you like it, just do a "frugal" install inside whatever OS your computer came with -- they can happily coexist. No need to do a "full" install -- I never have, and a frugal install has many advantages over re-partitioning your drive, etc.
Run WINE in it and you can run many Win programs (I use a few) though probably not AutoCAD. I use the old free Google SketchUP in Wine when I want to draw anything. There are enough free add-ons to that to do anything I want. It's definitely not AutoCAD though, and certainly won't satisfy an expert AC user. But for me, it's a breeze, and I get tons done with it quickly.
Anyway, just thought I'd mention another Linux alternative, relatively unknown, but immensely useful, compact, efficient, and timeless, in terms of what it will run on.
I do all my work on that.