Although the following video is making round in blogsphere recently, it is in fact an old news: A monkey at the Jerusalem Zoo has been walking upright after recovering from a stomach flu that nearly killed her [see also]:
Back in 2001:
Monkeys walking on two feet have long been an integral part of circus acts. The way they waddle from side to side appeals to our sense of comedy.
Now, however, Prof. Shigemi Mori and other researchers at the National Institute for Physiological Sciences have succeeded in training monkeys to walk erect smoothly, as humans do, by working with them from the age of 2 1/2 years.
Through this research, the scientists have learned that there is a considerable difference in brain function when an animal walks bipedally and when it walks on all fours. [source]