I use Windows and Internet Explorer and the 800 x 600 setting to be able to actually read the characters.
Your site, on many pages at least, is incorrectly sized as, on the above setting the left and right hand sides of the page are not visible nor can I scroll to them.
Using this smaller setting (75%) the page is fully visible but there are blank spaces on both sides of the screen.
Whichever way you set up a web site it should be either one thing or the other of the above situations except on your setup neither size actually works. All visible and no blanks on either side or partially visible but fully visible on the left and the right obtained but sacrolling across.
I've seen this happen on the rare web site where the builder fails to account for all potential users bu using what THEY LIKE. Not what suits ALL.
When told these web sites usually fix the problem. Can you have a look at it please?