Not quite sure what you mean, but if your goal is to set a default browser, is as simple as right clicking on a html page stored on your computer, select "Open with...", select the browser you want to set as default, and before clicking ok, check the box at the bottom of the dialog that says something like "set this as the default program for this type of archive".
If you have pages with both the archive extensions used for webpages, *.html and *.htm, be sure to repeat the procedure for the both types.
Hope it helps, cheers
edit: I just noticed that you're making the question regarding windows vista. It's pretty much the same, but you are given the option to select the default program right on the "open with.." menu.