There are couple of Chinese IME (Input Method Editor) for Chinese. I used Zi Guang as well as QQ, both of them are much better than the default MS IME.
However, it is very hard to find a good Japanese IME. Now, Google Japanese IME is available. I tried today, it is much better than MS IME.
It is very easy to install and use. For more details, I found this link is very helpful.You can also to go Google website to download directly.