Okay, I just tried it out and here's some suggestions (I'll leave code improvement to those more suited to it than I). Please keep in mind that these are my opinions only, so take that for what it's worth.
First out of the box, great job. Nifty little routine. Does just what I expected it would.
Second, too many prompts and not enough comments for my tastes.
Consider the user experience. How easy is this routine to use? For you, it's pretty straight-forward. What about someone who wasn't involved in the development? Is it intuitive enough for someone who clicks a toolbar button just to see what it does to be able to use it? And if someone has to use this routine more than twice in a 5 minute time frame, they'll get tired of answering those same questions each time.
Consider
your experience. If you dabble in LISP (a good thing, IMO) you will, no doubt, write more than just this routine. And you will, no doubt, still have this one somewhere a year or two down the road. As a person who dabbles (just like me!) it's very easy to forget why you did something the way you did it when you did it, especially if what you did was done a long time ago.
Cooments are your friend. You'll find that you'll learn more just from commenting your code. Explain what each portion does and how it does it. You'll find that, when you take that approach, your code will improve as you write it. Because things that don't seem obvious when staring at a screen full of code suddenly seem much clearer when you've got a running reference right there with it.
