How to use Unity Dash in Gnome classic?
There's Currently no way to use the Dash without Unity being active so here's an alternative.
elementary's Slingshot.
Slingshot launcher is developed by the Elementary team. Here is how to install Slingshot launcher in Ubuntu Natty from elementary team ppa.
Add the PPA ppa:elementaryart/elementary-dev and install slingshot-launcher from the software center.
To use it you simply have to create a launcher in the Gnome Panel with the command slingshot, the same goes for AWN.
Source.