Oh, another free image program which I like to always have around is Xnview. It's pretty good. It's not as "sharp" as Picasa, but it has LOTS of features and options. I don't recall how much pure editing you can do with it, but you can do all sorts of things with your pictures with it. I'm sure it also has an image resizing option as well... of course, part of what you want to do is resize the website images, probably for at least some of them, and then converting from bmp to jpg.
Really, either of those are simple tasks for modern programs. You should be able to do it with practically any program that offers any image editing. I mean, you can even just use MS Paint if you want - though it won't give you the best quality if you reduce the image resolution qualities, when compared with other image editors.
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"If to err is human, then I must be some kind of human!" -Me