No, there's no way to move or resize any open panels. (Unless there's a mod for that, but I don't think there were ever too many mods made for this game.) Just get used to closing your inventory whenever you're not using it.
That's too bad. I've noticed that Din's Legacy seems to have the same issue with the Inventory in the middle of the screen.
I'm admittedly not exactly super well versed in the various Diablo
-descended PC-ARPGs, but I don't think more than one or two of those I've played have the inventory in a side panel and/or let you move the window around. (The original Torchlight
does the former.) I can't imagine the inclusion of either of the above features became a very common thing in this subgenre until maybe the last four to six years.
It should also probably be noted that, as far as I know, all of Soldak's games -- going back some fourteen or fifteen years -- use the same (entirely homemade) game engine; the lack of moveable windows is probably something that the engine couldn't easily be made to support. (I've also heard that Din's Legacy
is supposed to be the last hurrah for that engine. Hopefully this is true, and the next project will be on a different engine.) It could also be that this wasn't a feature the developer cared about, and he never got enough requests for it from players of the "pre-release" versions during the early access phases of his last two or three games.
Out of curiosity: what's the problem you have with this? I can't say it ever especially bothered me that the inventory was front and center, so to speak, especially given that I usually had the game paused whenever I was doing anything much with my inventory or any other personal/NPC window.