The learning remote I have is from x10.com and the model number is UR24A. It was just a remote I had in my house that wasn't doing anything. The keyboard I have is a Lite-On SK-7100 that I use on my destop. (Works Great!) I don't really think it matters which remote control you use as long as it has "learning" abilities. Remotes that learn are becoming harder to come by as most remotes now just make you select your TV set from a list of codes. Also, the keyboard probably doesn't matter. I assume they all use a standard IR xmitter chip and unless they use some completely non-standard encoding frequency you'd be fine.
What I'd do is go for the cheapest IR keyboard you can find because you're probably just going to store the keyboard in the trunk and ultimately all you want is the reciever not the keyboard. Then, you can break open the plastic case for the receiver and mount it inside the iopener case just like people have done with USB hubs and ethernet controllers. You could drill a small hole in the iopener logo at the top and put the receiver eye in there. From there it should have good view of the remote control. I haven't done anything other than test that the learning remote can learn functions of an IR keyboard used on my desktop (non-iopener) system but I'm confident that if I built the receiver eye into the case I'd be fine.
As for the remote to use I've seen that a lot of people on mp3car.com are using the same remote control for their car MP3 players. I'm not sure if the remote has learning capabilities but I remember someone saying it was a $5 or $10 item so it's worth checking out. It was pretty slimline too like a credit card but a little thicker. Perfect for a car appliance.
I'm not making the iopener into a car unit. I'm going to put an IR receiver into an iopener and have it in my stereo cabinet at home. I'll write a frontend for an MP3 player that will work just off the arrow keys, the enter button and a couple other keys which will be programmed into a large remote that controls the stereo, TV, satellite, iopener, etc.
If you have any questions drop me an email: iopener (AT) deadtrout.com.