Laura - the first picture on the second post was not in the Flickr set. The Flickr page started with the second picture.
To watermark, PhotoShop is good for this. If you want a free, open-source complete knock-off of PhotoShop, download GIMP. I'm sure it's still out there, absolutely free. It was a few months ago when I downloaded it, but things change quickly in the open-source world.
Another option is Office Suite - Publisher (2007) allows you to easily watermark anything. You might also be able to do it in 2003, but that's no longer on my system so I can't say for sure.