It's quite simple.
Boba fett is the best bounty hunter ever*.
He isn't stupid and he knows the milenium falcon has no cloaking device for this reason he knows the milenium falcon is still around.
Now he would know that Han solo isn't dumb enough to travel trough lightspeed with the imperials as this would mean certain death.
So he knows that when the imperials disapear the milenium falcon will move and escape.
So to catch it he gets trown out with the garbage and this way he tracks the milenium falcon without being detected.
He's Willing to trow his ship in the garbage to catch han.
And by doing this he made a lot of $$$$$$$$$
Here is some information about boba fett
http://www.afn.org/~afn37335/bfett.htmI never read it but some "nerdies" might be interested.
*Some may say Jango but he got his head sliced off so....
MT