Some browsers not showing full page

I don’t wish to be unkind but this is a train wreck. I do not know where to start. There is for example a spare body tag half way thru.
I think this should be in 3 columns? Best to fit a more robust theme.
This is beyond repair.

Should I just pick out a new theme and load it and use that? A 3 colulmmn theme?

Is the problem with the theme and the way I’ve modified it?Or does the problem run deeper than that?

Three column themes can be tricky. Some folk can do them but explaining to somebody else in a forum for 3 cols is very difficult to do. Your situation requires a lot of editing. Can you roll back to an earlier version?

Yes, I reloaded the original apple theme, clean and the left sidebar still did not show up on the other browser. So, then I loaded blue-zinfandel, and it had errors too — even before I did anything to the template (according to the html validator) This has me worried — how could their be errors when I haven’t done anything to the templage — — is that even possible?

Yes it is. There is no quality control on themes. And many of them are *edited* by folk and redistributed. Validation is good. Without it IE will go into quirks mode. And God knows it is unstable enough already.
I think by going backwards you are making progress.
But 70 odd validation errors is ridiculous.

Ok — so the good news is that the problem is in the Theme and not my wordpress files. Is that right? And picking a new theme that is much more validated will clear these up?

Or do I need to start looking at my wordpress files to see what’s wrong.

You are right. WP does not have anything to do with themes or validation. So this is the theme that is the issue. Validation is important not because people say it is but because it is an important milestone to get your site to behave consistently in all browsers. Even that is not the end of it but it is a start. It is a steep and painful learning curve for many people. As a model you could track down moshu’s Vesuvius template and see how it works. (try Google).
Cut yourself some slack. Relax and enjoy the process. We are all beginners really.