If you mean that place on the north side among the hotels, it wouldn't be worth your journey. There are probably pictures and other displays in there but you'll probably not see many aeroplanes. It's a very low building and, although I've not been in it, I cannot see how you could view over the fence which is between the building and the airfield.
I don't know what to suggest as BAA have shut all "official" viewing areas due to "security paranoia". Local spotters know where to go to get good views, but it means driving round to half a dozen different areas.
If you are going to the central area by train you could go to the top of one of the car parks for views over the airfield. However, expect to be moved on fairly quickly.
If you just want to see aircraft send me a PM and I'll tell you some spots where you can watch landers and get good piccies...