I am wondering if there is a way to use Unity Dashboard in Gnome-classic? If yes, what are the dependency packages need to be installed?
Or is there any app could do that?
There's Currently no way to use the Dash without Unity being active so here's an alternative.
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
To use it you simply have to create a launcher in the Gnome Panel with the command
For Ubuntu 12.04, there is a way to get the Dash. However, this includes also enabling launcher.
You will get the unity launcher, from which you can open the dash. Or use the
For autohiding the launcher in 12.04 see this question: Autohide Unity Launcher in Gnome Classic.
I don't know exactly what you're trying to accomplish, but it is possible to run gnome-panel and Unity at the same time. Just don't use the upper gnome-panel, because that will create conflicts with the Unity panel. So just delete the upper panel and add gnome-panel to your startup applications, and you will have both.