I have almost finished third year university Japanese and next year will 
do fourth year. However, since I have started to find it difficult, I 
want to study Japanese in Tokyo for about one month during the 
Dec-Nov-Jan holidays.

Does anyone know of any good language schools where I could do this?

I found this one: http://www.wle-japan.com but I don't know if they have 
a good reputation. Is there anything I should look for in these schools?

Thanks for any suggestions.