Doch ... svn ... unstable section ... repos ...

I'm a newbie on gambas and this development process,
a gentle introduction please

Hehe, ok

Add the unstable repository to your slapt-get sources list in /etc/slapt-get/slapt-getrc:
SOURCE=ftp://ftp.osuosl.org/pub/vectorlinux/veclinux-5.8/unstable/
Update the package list and install the Gambas 2 IDE:
slapt-get --update
slapt-get --install gambas2
Then checkout the installer source code from the project's subversion repository:
svn checkout http://vinstall-ng.googlecode.com/svn/trunk/ vinstall-ng
After that, run gambas2, and select the "Open project..." option. Navigate to where you checked out the source code, double-click the source code directory for vinstall-ng and hit OK.
HTH