Have been surfing here for a long time and hope this time can write something to share.
This time I went to Tokyo for 7 days (in Dec 08) to relax and really hope to have the chance to see the 紅葉, so we went to one of the famous park in Tokyo - 小石川後楽園。 (just to avoid going to 箱根 because it takes more time and money.)
You can go to the park by sub-way or JR , get off at the nearest station > station 飯田橋 (JR or sub-way) or station 後楽園 (sub-way), and around 10 min. walk.
This is one of the nice parks in Tokyo so if you don't have too much time in Tokyo, but still want to see 紅葉, I would recommend this as one of the good choices.
Sorry that I don't know how to attach the photo so please see the link below,
[url=http://www.flickr.com/photos/10107359@N05/sets/72157612459232181/]http://www.flickr.com/photos/10107359@N05/sets/72157612459232181/[/url]
