Many thanks to you smart and helpful people - I've finally got this working. I was spending all my time checking and rechecking the code, and it seems that the problem (or the final one, anyway) was that the servo and PIC didn't have a common ground. And here I thought that breadboard with two separate bus strips would be *helpful*.

I did, at least, pick up a lot of PicBasic tips while working on this, so I should be better equipped for the rest of my project. Thanks again!