Ok... I'm looking at the Tips & Tricks section. Have you tried anything from there? I think these might apply:
Close Steam and then go to Programs>Run Command, select the Skyrim
bottle, enter regedit in the Command: field and press Run.
Within regedit, browse to
HKEY_CURRENT_USER/Software/Wine/Direct3D
in here, add a new string value called "VideoMemorySize" and
set it to "512".
If this has no effect, you might try going to back and setting
"VideoMemorySize" to "1024".
Should look like what's underlined with red in the picture below:
and this:
Turning off the 360 controller option in the settings menu if you
aren't using one. This gives the game a big performance boost.
Lowering the game's resolution and/or graphical details might also help. the GT 640M does not have all that much "oomph".
If neither of these tips work you can try asking for help from the staff via the ticket system.