Hi,
I just took a quick look at it (I did not know it before)

C-h f perldb tells me that it would start the debugger on the file in a buffer named *gud-FILE*. GUD is the Grant Unified Debugger for a small collection of languages. So maybe you should stick with that documentation (actually perldb is defined there; I don't have a file perldb.el at all). Furthermore it asks me how to run the debugger in the minibuffer. I tested it under XEmacs and Emacs in fairly current versions

If this is all trivia to you, please excuse, if you'd like me to have a closer look at it, just message me in the CB

Regards

Stefan K