I experience extremely slow frame rate playing HoMM IV in 1280x1024 (highest resolution) though the slowdown is only slightly noticeable in 1024x768 and inexistent in the lowest setting. My setup is:
Phenom II X6 3.3GHz
8GB RAM
GeForce GTX 550 Ti
Asus Crosshair IV Extreme
(and a conventional Seagate HDD temporarily until I get my SSD working)
Windows 7 Home Premium SP1

Another problem, that I've no idea if it's connected to the first one, is that the lowest part of the screen (which is in detail: the hourglass' lower half, the lower screen border and the area where the months are shown) is not visible. As if it doesn't fit the monitor or something.

I've tried everything, including all driver and DX updates, playing with admin and compatibility settings (by right clicking the executable). This doesn't happen on my brother's laptop but does happen on my computer.. Playing at a lower res doesn't constitute a solution for me. I need some help!