Thanks, nice work. Just picking nits:
The final bit about this procedure involves the input parameters. I chose to use TinyInts for these fields to permit a value of 0, 1, or NULL. I catch this in the where clause using case statements.
That's a case for the data type bit (http://msdn.microsoft.com/en-us/library/ms177603(SQL.90).aspx). You can then use ISNULL or COALESCE when checking their values, that's shorter.
Also, calling the first parameter @ShowSystemProcesses might be more intuitive, as in that case both NULL and 0 would have the same meaning.