I've bought the game here yesterday and tried playing it on my laptop first, where it ran perfect. The screen had black borders on the sides so it wasnt widescreen stretched, mouse worked fine, no issue.
Just now I tried it on my gaming desktop PC where it is stretched out to fit widescreen. Additionally, the mouse was glitching out which I found out you can get rid of if you turn off enhanced pointer position. Also the cloud saves dont seem to work but thats not really a biggie.
I've found out how to put the game into windowed mode but I'd really rather play it full screen with the regular resolution unstreched. Both machines run win7, both should be updated, both are widescreen screens (just different resolutions) with the only difference that laptop runs nvidia gpu while PC is an amd.

Any ideas?

You should either go with the HD mod which gives many options regarding resolution.
Otherwise, creating a specific profile for this game in your GPU driver and choosing to keep aspect ratio is the only other way to do it afaik.

Thank you, updating drivers and choosing to "preserve aspect ratio" has done the trick. incidentally mouse jittering stopped too.

Cool. Do consider checking the HD mod mentioned above too
https://sites.google.com/site/heroes3hd/