Its interesting how you can ask a simple question and all of us try to put on lawyer hats.
Cruise control is actually quite difficult. Forget all the (how do you turn it off stuff for a minute).
Think about how much do you need to accelerate when you are not going the desired speed:
What if you are going up hill?
What if you are going down hill?
How powerful is your motor?
How much "gas" do you give it when you are falling behind?
I have a project where I have been trying to tweek these things and it is difficult.
For any vehicle, it is different depending on what speed you are going... You can give more acceleration at low speeds than you can at high speeds.
Its loads of fun to play with this type project. The interface to your 0-5v is the EASY part.
PID is what it is all called. Great reading, etc.
Google PID for more.
Try asking us here for more specific interface info, like-- "how do I generater a 0 - 5 volt signal to adjust the throttle on my engine?"
How do I measure the speed of a rotating shaft and turn it into MPH?
Greg