"untested" was not a repo source when 7.0 was assembled. It can be added. As root, edit /etc/slapt-get/slapt-getrc. Add the following line somewhere in the first, ohhh, seven lines or so:
That adds the repo as a source FOR 32-bit 7.0 VERSIONS. If you're running 64-bit or 7.1, just modify the line according to hata_ph's links. Now restart GSlapt and enable/disable it, or do so with a text editor.
Keep in mind that packages in untested are purged weekly, so if a mention is more than a week old it's either been moved or simply deleted. The buildscripts are still present, so if you're interested in a particular package that might have been purged, ask in its thread about it.