Sorry to reply to my own post, but maybe the problem is that the (then) hidden mouse cursor reaches the edge of the program window and sort of stops, making mouse movement stilted in the game? I have no idea, but it's just a thought. In Preferences>Input I have 'Ungrab when cursor leaves window', 'Hide cursor on ungrab' and 'Grab when cursor enters window' all unchecked, but they are the only mouse options I can find and I can't see that they would make any difference regardless.
Edit: It's definitely the hidden mouse hitting the edge of the program window. It only appears to happen in full screen, when I have it to 'stretch guest'. This is somewhat annoying since this is what I'd like the options to be on! I also have the odd thing of buttons (walking, for instance) lasting longer than I press, but that's for another time 
There is an option where you can allow 3d applications to keep mouse. I'll try to look it up, but that's the setting, so google "allow 3d applications mouse vmware" or search however u would 
sorry not to have a concrete answer
I've had a look but can't seem to find that option (I only found an option to "Disable acceleration", but that's not checked). This is for version 6.04 if that makes a difference. Could any kind soul point me to it, or offer more advice?
As I say, I 'hit' the edge of the screen with the invisible cursor, but also mouse movement is pretty crazy generally in FPS games.
Edit: I found this "To enable 3D acceleration, shut down (suspend doesn't count) the virtual machine and go to Virtual Machine > Settings > System Hardware > Display. Check the "Accelerate 3D graphics" option", but my options do not have this. All I have in that list is: 'Use host setting for monitors' or 'Specify monitor settings', and all the latter has are 'Number of monitors' and 'Maximum resolution of any one monitor'. And there's no mouse options in there either.
