I have created a simple Excel spreadsheet that will help you solve your puzzles. Basically, as you enter in numbers in the grid, it will remove them from the relevant "pencil marks".

I wouldn't recommend using it with the "easy" puzzles as you will be able to complete the puzzle with absolutely no thought power whatsoever, but it might be useful for the more tricky ones.

Here it is...

http://www.hifi-remote.com/sudoku.xls

Each Sudoku cell is represented by 3 Excel cells (arranged vertically) where the middle cell is the one where you enter your numbers. The smaller cell above will automatically calculate what numbers remain valid for this cell based solely on the vertical column, horizontal row and box. It doesn't try to look for doubles, triples, etc (after all, some of the fun has to be left to the player).

The smaller cell below the entry cell is where you can enter numbers that you have determined are not valid for the cell. These numbers will automatically be moved from the valid list.

Enjoy.