Hrm, my previous post seemed to have been deleted. There is a nice circuit for this on the web already. There's a book called "Intermediate Robot Building" and it has a robot the guy designs that drives around and avoids obstacles. If you do a google search for the book, you'll find his website, on which he has a circuit to produce a 38kHz infrared signal which could then be detected by your TSOP1738
Had this all in my previous post, maybe it got deleted because it had a web link in it and it was my first post? Dunno, thought it was really helpful since it was spot on for the project you're working on. I built a quick circuit on a breadboard last night to do just this kind of thing you're talking about. PM me and I can send you more details if you like.