That's a very nice concept in fact, and I think it's very possible to make such skin. The only thing I know you won't be able to do is the semi-transparent border around the window. This is because of the way Messenger draws its windows, they're drawn on a child window and thus the result must be fully opaque. I don't know if it's possible to align the "Search in contact list" text to the right, and I also don't think it's handy to type right-aligned in that box. As for the rest, it looks very doable.
I'd love to help you, only I haven't skinned in years and I still need to find time learning it again using the new techniques Plus! Live offers. But I hope that someone will find this topic and give it a try. Or you can try to learn skinning yourself, if you want. You can always ask help on these forums, but remember to search first!
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