I noticed some lack of 'acceleration', i.e. not lag as such but the cursor not moving quite as much as it should proportional to mouse movement, at the highest resolution (1600x1200).
This can be fixed on my system by going into Windows' mouse properties and increasing acceleration.
On XP with (default) control panel category view :
Start->Settings->Control Panel->Printers and other hardware->Mouse->Pointer Options->"Select a Pointer Speed" slider->Apply
On XP with control panel "Classic view" / win2000 / win9x :
Start->Settings->Control Panel->Mouse->Pointer Options->"Select a Pointer Speed" slider->Apply
I have to drag it most of the way to the right, your mileage may vary. Also you obviously have to drag it back after you've finished playing unless you like a high speed windows cursor.
This is on a XP2100+ / 512MB / GeForce 6800XT so I think it's purely a resolution scaling thing, the game plays smooth and looks great