[ros-users] How could I compile packages from trunk

Hi all,
I downloaded packages from trunk for testing. In order to build them, I
must do these following actions:
In another folder not in trunk, i create a new package. I do it so that
ros knows where my package is.
- roscreate-pkg <name of package in trunk>
Copy all files of the package in trunk to the new folder.
Do rosmake in the new folder.

These actions are very complex because I must build all depending packages.
Are there other method for building packages in trunk?
How ros knows the pakage existing in a folder rather than using
roscreate-pkg and copy/paste?
Thanks.
Thuan.