Again, what exactly is grayed out? Here is the screen where you have to enter your credentials to access MobileMe:
You should be able to simply tap on the field where it says "Name" and start typing, and similarly the "Password" field.
If you are seeing something different, can you capture an image and show us? Hold down the button on the top of the phone and the springboard button simultaneously to capture a screenshot to your Saved Photos album. You can email to me (@gmail.com) if you don't know how to attach to a forum post.