Thanks for the reply.
The reason I wanted the site to 'snap' from one size to another is that on one page I have four columns of text. As the browser window narrows the text columns look too squashed and I don't like the appearance. To avoid this situation I thought it would be best if the site would not be allowed to narrow so much before it alters layout.
Regarding DW, it creates three layout sizes (desktop, tablet, and mobile) with fixed breakpoints. According to my 'Missing Manual' book, these cannot be altered without breaking DW's layout system.
Your advice to ditch DW sounds good to me as I can envisage a situation where I am tied to the software. I was previously in this position with Serif WebPlus which is easy but not good code apparently. So far I have been using design and code view in equal measure, realising that code view is beneficial for learning. It would be nice to stop using DW as so far I reinstall windows from a restore image when the DW trial ends then reinstall the trial.
With a responsive site how would you ensure the site always looks exactly as you wish? Do you create lots of breakpoints to avoid squashed content or maybe even layout the content so that squashed columns would not exist?
Do you design your perfect layout and then make it responsive or do you design the layout so that it lends itself to being responsive in the first place?
Does that make sense?