Hi Artress,
I was taking some time off.
You can use the 2.1 version in Joomla 1.5 but in legacy mode.
The New version 3.0 will support Joomla 1.5 fully.
Please understand that nightly builds of Joomla 1.5 don't aways work.
It very close to done but changes happen that break the system from time time.
I can tell you that the Joomla Template kit 3.0 is coming along great it will be a enjoy to work with or so I'm hopping you all think so. When you get a crack at it soon.
Cheers,
Brian