Should I walk or take the train?

On day one I'll be visiting Asakusa, Akihabara, the Imperial palace, and ginza. Should I take the train between these places, or walk? Any of them have good sights between them? Or should I maybe walk some and train the others?

I'll also visit shinjuku, harajuku, shibuya, and roppongi... Again when should I walk and when should I take the train? I know its personal preference, but are any of the walks totally worth it, or are any of them totally lame?

On day one I'll be visiting Asakusa, Akihabara, the Imperial palace, and ginza. Should I take the train between these places, or walk?

Most of those areas are relatively far away from each other, and involve a lot of walking already. I'd rather take the train, and save my energy for exploring the districts instead.

I'll also visit shinjuku, harajuku, shibuya, and roppongi... Again when should I walk and when should I take the train?

You can walk from Harajuku to Shinjuku via Shibuya. It can take up to a full day though. Roppongi might be better accessed by train.

You might be interested in this walk:
http://www.japan-guide.com/e/e3051_west_tokyo_full.html

Or this page:

http://www.japan-guide.com/e/e3051.html