If your recommender has no idea how to write these things (or has little experience writing business correspondence), by all means do so. Just be judicious in how much (or how little) info you give them in the package you send them.
The #1 thing with rec letters is this -- making it as easy as possible for your recommenders to write the letters.
This means to avoid inundating them with reams of info that it overwhelms them. No one will read 10+ pages of commentary plus sample letters and so forth. If you don't know what to include, resist the temptation to just throw everything and the kitchen sink at them. The pertinent material will simply get lost in all the junk. And if you don't know what is pertinent and what is extraneous, then that's what you have to figure out first before sending them anything.
On the other hand, don't leave them hanging either by providing zero info either. Your recommenders may know you extremely well, but you'll make their jobs far easier if you refresh their memory of a few key examples that complement or reaffirm the examples you talk about in your essay.
So keep your info packet succinct - and your recommenders will also more than likely be succinct in their letters as well - and everyone (including the adcom) is happy.
Good luck
Alex
alex@mbaapply.com
www.mbaapply.com
http://mbaapply.blogspot.com