Thank you, Laydewlf, I got it to work! I really hope there is an easier way, lol.
Bowsbymomma - I used Gimp. I opened my image, then opened my watermark as a new layer. Then I used the resize tool on the new layer until it was he size I wanted. Then I used the little move tool to put it where I needed it. On the toolbar thing that shows you the layers, there is a transparency slide bar thing (near the top) and I just moved it over until it was the transparency I wanted. That was it!
Not as bad as I expected, but I am so not comfortable with Gimp. I really need to learn how to use it, I hate not knowing how to do things well.
And I apologize for my crappy explanation, I obviously don't know what I'm really talking about, but hopefully you'll understand what I mean.