CG iPhone™

Backgrounder is a tweak available on Cydia and necessary for all jailbroken iPhone or iPod Touch.
It will then permit you to manage multitasking (you can have several applications running at the same time).
Start one application
Long pressure on Home button, the application is now in background
Long pressure again to disable the backgrounding.
Since the version snv.r330-3, use Activator to background an application