Unfortunately on EWBF dev page is stated that the ZHash algo (Equihash 144,5) needs at least 2.2 Gb of GPU ram, thus mining of BitcoinZ works only on GPUs with 3Gb or larger memory.
Unfortunately I can not use my 2GB VGA, it was fine in how long it lasted.
The new miners in development may support 2GB cards. I believe they said they can get the memory requirements down to 1.7 GB, which will fit, so keep in the loop.