Good going, Val! It looks great, but I have a suggestion which you might not have thought about. Like many others, I learned to check sheets using IE and Firefox... but I didn't bother viewing my sheets using different screen resolutions until someone else mentioned it. I've found it's always a good idea to, especially since so many people are going to newer, larger monitors.
I'm running 1280 x 1024, and see your page with the thumbnails pushed to the left with blank space on the right. So, you might consider "center" justifying them.
For anyone running a PC, changing the screen resolution only takes a second. Just close your browser, and "right click" the blank screen. On the pop up menu, click properties, then settings to make the change.
For "mac" users, I'd suggest asking Andrys. Sorry, I'm not familiar with it myself.
Might be good to check the page beginning with 800 x 600, and work your way up. While theres only around 5% of users still using 800 x 600, it's inviting to them to see a site where they won't need to scroll.
Keep up the good work.