Do you mean set the focus of a form field within Dreamweaver's Design View interface?
There's no built-in function of DW that I've ever seen, I'm still a few versions back. It's "possible" it was added, but I don't see this being in such common usage that they would add it though.
Really? I would think this would be a super common request. Basically any webpage that has a form... even a login page, to have the cursor ie focus set to the first field.
The snipet piece would be difficult because the field name would be different for each page.
How are you currently setting focus of your elements?
If you use HTML5, you just set the autofocus attribute within the actual form element and you're done. It's the same no matter what page, form or user input you set it on: autofocus="autofocus"
The script for that is extremely small and very simple.
In all hosety, it would probably take longer to edit it through the DW interface than by hand.
Add this after your form and change the bold areas to the name of the form and the name of the input you want to have focus on...
Those two things are the only items that will ever change.