Normally I don’t do this, but since this is such a great article:
http://blog.getpaint.net/2008/12/06/a-fluent-approach-to-c-parameter-validation/
From the creator of Paint.NET.
It’s really worth reading, if you do a lot of parameter validation. It might come in handy for your forms, or maybe even for a website.
I think I’ll write something based on that really soon 
Believe me when I say we have a difficult time ahead of us. But if we are to be prepared for it, we must first shed our fear of it. I stand here, before you now, truthfully unafraid. Why? Because I believe something you do not? No, I stand here without fear because I remember. I remember that I am here not because of the path that lies before me but because of the path that lies behind me.
It’s a movie, but I think the last sentence applies to everybody. It’s your decisions that makes you who you are.