Plug in your phone and click 'Explore' in ActiveSync. You'll see this window:
http://img25.imageshack.us/my.php?image=ps1e.jpg
Double click "My Windows Mobile-Based Device". From there, click 'Tools' > 'Folder Options' then the 'View' tab towards the top of the window.
http://img150.imageshack.us/my.php?image=ps2b.jpg
Next click the bubble by "Show hidden files and folders", then apply.
http://img527.imageshack.us/my.php?image=ps3.jpg
You'll be back at your main window, double click "My Windows Mobile-Based Device" and now your Windows folder will be visible
http://img527.imageshack.us/my.php?image=ps4.jpg
Be ready for a wait when opening your Windows folder. Depending on how much you've done with your phone, it can take 60+ seconds to open.