I found my own solution. I am in no way certain that it is the correct solution, and if anyone else can tell me how they are doing it, I would surely appreciate it. I might as well learn it correct from the beginning :)
So what you have to do in order to launch a tour that automatically shows 100% of the browser window no matter which screen resolution the user have is:
1) Deside the minimum screen resolution you want to design for. I don't believe anyone really still uses 800*600 so I will design for a 1024*768 window (guess it should be smaller as the browser window never display 1024*768).
2) Build the tour as you normally would in the 1024*768 window.
3) When you place any features as thumbnails, map etc. remember to use the alignment tool
4) Publish your tour as you normally would.
5) After you have published, open the "TourWeaver_XXX" file in an editor (dreamweaver, notepad or whatever you are using)
6) In line 15, find the place where the size is indicated (look for "1024", "768")
7) Change the numeric size to percentage so it now says "100%", "100%"
8) Save the TourWeaver_XXX file
9) Double click the TourWeacer_XXX file and see your project in 100% of the browser window - no matter which resolution you are using - as long as it is above 1024*768
The downside is that your graphic elements will be stretched.
I haven't really tested this approach so please help me and report any problems you might have doing it like this so we can all learn from it.