I have Samsung galaxy ace with android 2.2 mobile.

Is there any way or any application so i can run many applications simultaneously and i can switch among them?

**Why do i need this.**

1. When i surf facebook(or any other
application), and i click on a link.
I am suppose to wait until the page
gets opened then i read it pess back
button to reach on previous button.
If i press previous button in
between i'll lost page which was
being loaded.
2. If i read some sms, and i have to
search the meaning of a word in dictionary, i
would have to exit from sms box.