My website looks funky on a Mac...how to fix?

Hello,
My website (www.nebraskasky.com) looks okay in internet explorer....however, on a macintosh...the top line of text isn't straight..it looks very unprofessional. (On the Mac and PC, I was viewing both in internet explorer....so I don't know what the deal is.) How do I fix this? Any ideas?
Also, I designed my site for a screen resolution of 800 by 600 pixels..I heard that is most common screen size that people have their computers set at.
However, everywhere I have been going lately...everybody has their monitor set at a higher resolution...so instead of my site looking impressive with all of these large, full screen pictures...it looks small and up in the corner....It doesn't look so great. If my pages would show up at least in the MIDDLE of the screen...not on the upper left corner, I think that would look better.
If anyone would have an idea or two to share towards a solution, I would appreciate it.

Apparently the Mac is displaying it more accurately than the PC.
Try viewing the site with a standards based browser like Netscape or FireFox and you'll see that the top line is not straight there either.
Without taking a closer look I'm not sure why but it probably has something to do with your setting some td heights different than others.
Also, if you're trying to code for an 800x600 screen - why do you have a td width of 1008?