Not only is the whole idea of taking the human element out of overseeing the voting process,those little old ladies who help out on voting day do a very good job and they are not as simple as some might think,you'll have to work hard to pull the wool over their eyes, and secondly there is just no way that you can ever make these machines tamper proof,wether in the design stage or when they are out in the field.basically if the manufacturer says that the alogrithms used are proprietry then thats because they have something to hide and they dont have enough confidence in them to have them open to public scrutiny.
A very respected cryptographer Bruce Scheiner says that the whole idea of a secure voting system with mutual athentication and verification is utterly impossible to achieve.
there is only one reason why people want to implment electronic voting and that is because it is so easy to cheat.