Here's my view, as the webmaster of team 254's page (
http://dagnabit.org/~krazikamikaze/newrobot):
The layout can be done by any amount of people, depends on how many are on the web page subteam.
The graphics can be done by whoever's good with graphics, just assign them a graphic to make and have them make it. The only problem I can see with this would be if you are designing a graphical interface for your website that has to fit together perfectly (for example, our website). There must be about 20 images that make up our website's border, some of which are as small as 100 bytes. This should be done by either one person, or two people working on the same computer. That way when the layout person finds that he/she needs another image to make the layout look right, they can have the graphics person do it, or just do it themselves.
The HTML coding can be done by several people (who know how to do it, of course). Each person can work on a seperate page, just make sure that each one understands the layout and knows what template they should follow.
The other coding (perl, php, asp, jsp, etc.) should be by 1 or 2 people. The problem with having many people working on this is it is hard to understand another person code because it is usually very complex. It is best if only 1 or 2 really good coders work on that part.