[OT] Help needed with computer control of hardware

I apologize for the off-topic post, but I know there are a bunch of 
folks on the list who have invented this wheel before...

I'm working on a project (not a rocket, alas) where I'm going to need 
to do some (basic, I think) control of hardware from a computer. I'm 
going to need to drive stepper motors, operate solenoids, and read 
pressure sensor data into the computer. There may be other kinds of 
things that need to be controlled or sensors to read data from as 
things go along. The project does not require a real-time control 
system.

I'm looking for information on how to start learning how to do those 
sorts of computerized hardware control. Books? Websites? When is it 
best to do the control in software and when to offload it to a 
microcontroller? RS-232 or some sort of dedicated digital interface 
(there seem to be a myriad of choices). If it matters, the machine in 
question will most likely be an XScale powered PC104 SBC running WinCE 
.NET 4.2.

Thanks!

-Pete