With this and Buildcraft pipes we can make this:
EDIT: New version of the video, with fixed audio and better quality.
I used the distribution pipes from Additional Pipes mod (previously called Teleport Pipes). As you can see, I added a small part on the end of the video about using Redpower 2 logic blocks to make it fully automated (so we won't need to do anything but receive the stuff). However, I left a mistake on the video and put a comment on the description telling the people to come here and look at the fully functional version. I know, I'm evil... or a little annoyed with the people who don't bother looking the description. So here it is, the solution to the enigma:
As you can see, I added two logic blocks and some cabling between the piston control and the planting control. The toggle latch will allow the timer to start working once the pistons unpower (and release the water), so that timer needs a value equal to the time it takes for the water to take all the wheat and seeds to reach the collecting channel and dissapear (it will be different for each farm, depending on how long they are). That new timer will repower the toggle latch (blocking itself) and start the planting process.
And for my next update, I promise you an infinite source of pneumatic power using combustion engines. Equivalent Exchange and lava are involved, and the release will be first in this blog (with a video, of course), and some time later in my youtube channel.
Edit: Since I had a crash in the game, I can put a full list of my mods, here you have it ^^
modLoader Beta 1.8.1
mod_AdditionalBuildcraftObjects 0.5b (MC 1.8.1, BC 2.2.4)
mod_IC2_AdvMachine v2.1 modded by CPW
mod_mocreatures v2.13 (MC 1.8_1)
mod_IDResolver 1.8.1 - Update 0
mod_TooManyItems 1.8.1 2011-09-27
mod_WorldEditCUI v0.9.1 for mc1.8
mod_RecipeBook Beta 1.8