first of all, @jacksawild: please don't be too angry about all of this, I've read the thread again and some of the comments sound quite harsh to me. I think your general idea is quite good.
tooltips for soldiers in inventory: I think the way it's been done before with UFOextender is better as long as we have 320x200 pixels. have the relevant stats displayed to the top right of the soldier - the rest is accessible via clicking the rank icon anyway.
tooltips for weapons: I don't know... I don't think you need that information always at hand. perhaps this could be done by integrating the ufopaedia into the game better? if you right-click on an item that has a UFOpaedia entry, you get a one-button popup window "show UFOpaedia entry for %1", which takes you there - clicking outside the window erases the pop-up? that way you could access the information you want.
tooltips for UFO's: you are aiming for some air-traffic-controller type of info, right? I like the idea, but I'm not sure what I would want to have displayed, considering that in the original 320x200 you could only have one or two lines of (short) info there, else everything would look all cluttered. plus most of the really relevant info is only available after you have a hyperwave decoder. of the basic radar info, what do you really need?