After a little googling i've found a nice and small (only one 1,36M exe file !!) 3D modelling sw.
It is here:http://solvespace.com/index.pl
A useful demo video from the site:http://solvespace.com/vids/demo.wmv
The free downloadable version is light (shareware):
"As downloaded, SolveSpace does not include a license key. For the first thirty days,
the program will run with no artificial restrictions. After thirty days, a notice will be
printed in all exported files." That's all !?
"This light version of SolveSpace is intended
for evaluation, but non-commercial / personal use is also permitted."
The 1-User License is only 79 USD (really not so expensive : - ).
I did not try it but I hope somebody will find it useful.