Never made any custom content before? Start with the easiest, most basic stuff (which you can make with all free programs) - Sims 2: Walls, Floors, and Ground Cover, Sims 3: Custom Patterns
Just installed the Sims 3 patch or about to? Read this article for helpful advice about patching and keeping your custom content working!
I have been involved with computers and engineering a long time (I was excited when Popular Electronics first published a story about a 'personal computer' in 1976 which had a whole 256 bytes of memory). I no longer work in engineering, opting instead to raise cattle in central Texas.
This is the seventh calendar year that I have been fascinated with 'modding the Sims 2', and helped decode some of the mesh data types, and I wrote and maintain the Sims 2 mesh plugins for the MilkShape 3D editor. I have now moved to The Sims 3, and I am working on various mesh and animation doodad thingys.
Oh, and that gal shown to the left is a cow named Lady, one of a breed called Texas Longhorn. And they are.