Brandon,
In my opinion, you have nothing to be ashamed of with this site. It looks good, is well organized, and presents your products well. Having said that, and since you seem to be interested in "professional" results, I have a couple of comments that are meant to be only constructive:
1) You might want to rethink how you accomplish your layout goal. CSS could help you acheive your "Centered" much more efficiently and allow the site to "resize" and remain centered on 800x600 screens. It might seem lilke a big project, but the results will (IMHO) be worth it.
2) You can "kick it up a notch" if you will consider abandoning the image based rollovers in favor of CSS driven "list" menus (check out listomatic on google!), since your images are essentially "text" anyway. This should give you better search engine friendliness, looks cool, and is very easy to change should you need to add additional links as your site grows. The JS is well done, but there are, I think, better ways to do it.
3) I think you should be more careful about your use of centered text, rather than "left-"aligning it. For some things, it looks ok, but multiple centered paragraphs get hard to read, and don't have a polished look. Looking at your "installation guide", if you try left justifying, or using a "list" for the section links, I think you will be more pleased with the results.
Enough criticism (and I am only trying to give feedback)! The site is well done and I think the fact that you did this site at your age shows you learn well, care about quality, and have great potential. I have seen a lot of sites around the web that people have spent a lot of money on that are not as nice as yours and do not show their busines in as favorable a light as you have here.
Good Job!
rlparker