I used the GetAsyncKeyState command to check if each button was being pressed, then moved the player accordingly. I ran all the game code in a semi-infinite loop with a very short Sleep to limit the framerate, with DoEvents enabled to allow key presses. I think I commented the VBA code if you want to take a look with ALT + F11. At the start of the project I imported the GetAsyncKeyState and Sleep commands from somewhere outside of VBA - I think they're system-wide properties?
Have you bypassed all the warnings PowerPoint shows like enabling editing and macros? Sometimes it helps to open the VBA code for some reason. If it still doesn't work, then I'm afraid that's all I'm willing to do at this point. PPT Jam was a long time ago in a program not at all suited for game development, so I'd rather move on to new projects at this time.