I also use the FP forms (should really look into getting scripts).
You no doubt know you have three options with a FP form, and as I mentioned in sticky, one of the possibilities is a DB. If you can use any sort of database it may be of advantage in future and an easier way to sort what will be an increasing amount of feedback.
Anyway, here is a solution you can do with Frontpage since you say you are used to it, perhaps (almost sure) its not the best way - but a way at least.
Instead of posting the form to the guestbook page, send them to the default file that FP creates when you make a form (the text file).
Create a "confirmation page" with frontpage and make sure on the original form you point the form to this "confirmation page".
On this page, this is where you want the business to be done. The form will post the form variables on to the page. From the same page it can then be determined where it is to be posted to depending on what lake was checked using a scripting language.
It would go something along the lines of "post to ____.htm where the page equals the "lake" form value. On the same page, you can then redirect/post to the according lake page depending on what the user posted and their choice of lake
Basically, its an awkward way of getting variables from a form without mucking up the FP webbots and adding on a script to tell it what where you *really* want the results and viewer to go and the information to be posted to...without all those excess forms.
It is almost impossible to tweak your own code in Frontpage in regards to webbots- so there is no easy solution.....but if you could get the form to point to a confirmation page using FP (not hard), then someone can post the necessary script to be included on the confirmation page.
Hope your following me on this.....I think I can write the code needed in the example....let us know if you can get the FP form to do the above- unless someone has a simpler way...no doubt a non-FP way ;)
Hate to sound long winded, but FP can get in the way of what would be a simple process to someone who has learned their stuff not using the prog