If you mean the OpenSprinkler 1.x generation hardware, yes, Arduino 0023 in Linux is still the preferred software. The firmware for the upcoming 2.0 will compile in Arduino 1.04.
I just wrote a blog post this morning about a VirtualBox image for compiling the current OpenSprinkler source code. Basically I’ve created a virtual Linux image file with all the necessary software and tools pre-installed, so you can use it with VirtualBox for compiling the source code. The blog post is here: http://rayshobby.net/?p=6149