GitHub keeps the entire commit history. You can go to the history list and download a previous version of the repository. Here is the direct link:
https://github.com/rayshobby/opensprinkler/commits/master/OpenSprinkler%20Controller/software
I think the version committed on June 19, 2012 should still work with FTDI programmer. However, since you have an ISP programmer, I would recommend you to upgrade to the latest firmware (1.8.2). You need to solder a 2×3 pin header to your v1.0 board, and then you can upload a .hex file using your ISP programmer.