Designing a website is often a trade off, because there are so many different variations of browser, screen resolution and operating system. If you had the time and resources, it would be great to create a dynamic website that determines what browser and screen resolution the user has and then delivers a website specifically for them, but for most businesses this is not feasible.
The strategy I would suggest is to optimise your site for the majority. Make sure it still looks ok and functions for other configurations and then don’t worry too much about the negligible minority.
So how do you find out who the majority is? There are a number of sites that give statistics on this. One I use is w3schools. It also shows historical data, so you can try and see where the trends are going, so you can also consider the future.
Using this I would recommend the following
Optimise for MS Internet Explorer (both IE6 and IE7) – 55.6% but make sure it also will look good in Firefox – 31%. Don’t worry about Safari unless Mac users make up a significant part of your target market.
Optimise for 1024 x 768, ie the design should fill the screen but have no horizontal scroll bar on a PC set with screen resolution 1024 x 768 with the browser website maximised. It should still work for 800 x 600, but a horizontal scroll is ok, and on screens larger than 1024 x 768 the design should be centred in the screen. It is ok for the content area to stretch to an extent, but it stretch to the full length of the screen, then on large resolutions, you end up with more than 25 words per line which limits the ability for the user easily read the copy.
A word on Mac’s.
While Mac’s are gaining popularity they still make up a very small proportion of internet users (3.5%). This 3.5% is then heavily made up of people in the graphic design, advertising and creative industries. If you want to attract this market then it’s important to consider this market when developing your website. If you don’t want to attract this market then your probably better off spending your time and resources on improving your website for the majority of users.