Anything is possible.  What errors do you get?

Directory structure needs to be identical as you found out.

The image issue could have been a cmyk color profile on something that needed rgb. It happens with other file types, I'm not sure if it can happen with a .png though.

Only some servers have that type of case sensitivity. I can't remember exactly what it is that causes that (none of mine have been set that way). Some good rules for file naming is to avoid spaces, capital letters and special characters other than the underscore or hyphen.

Your image gallery seems to work fine here in IE9. I also checked it in the IE7 and IE8 modes and it seemed to work correctly.

Google will eventually index your website, but it can take a while. If you just uploaded it for the first time, you probably won't show up in Google for 2-4 weeks or so.

Whether code validates doesn't always determine whether it works or not. All of the browsers have been programmed to essentially guess what was meant when they run into coding errors. IE seems to be the worst at that. Some coding errors are only "technically" errors because they belong under a different Doctype declaration (using > when you should have used /> instead), others are flat out wrong with missing info, but still work because the browsers "guessed right".

You can have hundreds of validation errors on a page (Adobe forums) and still have a fully functional site. It's just best to validate, make sure none of those errors are show stoppers, and fix everything you can to make sure finicky browsers (I'm talking to you IE) don't get mad at your page and give up trying to display things correctly.