Look for opensource utils, such as FreeCAD, Blender (mentioned and highly recommended), or OpenSCAD for mathetical based stuff.
I primarily use OpenSCAD as it guarantees manifold models for use in 3d printing, but you do everything functionally...want to draw a cylinder with a hole in the middle?
cylinder(r1=1, r2=5, 15, center=true);
cylinder(r1=0.5, r2=0.5, 16, center=true);
...you get the idea
Want to get hardcore and do some FEA? CAELinux is available as a live CD (you can boot into the OS with the app loaded, but you can't install in Windows), and supports fluids. I don't have any experience with this util but it looks effing sweet.
Most opensource CAD and modeling programs will work in Windows as well, and if you just can't get it to work, maybe it's time to make the switch
(or you could just dual boot...or use Linux with WINE for your Windows apps...etc)