davee5 has some good suggestions. I would definitely prepare your page for a 800x600 fit, for those users who still use smaller monitors and that resolution. Not to mention it will always look better for someone at a higher resolution too. Possibly may want to make the text one size smaller, would need to check it on an 800/600 page and then on larger resolutions to see how it looks. Condensed, organized, and readable is your main goal.
If you use the pics on the main page as links make sure they link to something appropriate, not just to any other page in your website. The pic with the link should tell a visual of where you would be going without them having to read around it or a caption. Pop-up not description can be added to the pic using the "alt" attribute for the image. What a pic of all three guitars together as the gallery pic?
Put your text and pics in tables, this allows you to really place them anywhere on the page.
+1 on the centered text, that looks best for headers, titles, and quotes only.
For the front page i would shoot for a single picture frame in the middle that did a slideshow of the six pics you used and if the you click any one of the pics it will take you to the gallery page. Lets face it you want them to oogle over the gallery pics then click for pricing.
Don't forget reverse navigation, once they get to a page better make it easy for them to get back to the main or whatever other page they want to visit. I would add a smaller font/simple text nav bar at the bottom of each page, i.e. "Home | Gallery | Pricing | Contact Us"
I wouldn't do the mouseover picture change effect on the guitar pics on the gallery page, instead do maybe a border change for each pic. I like the color pics, not really the B&W. A little more description for each guitar too. Love the new window for the photo gallery of each guitar, good transition too for picture viewing, plus they can just close the window and be right back on the main page for that guitar. Change the titles for your picture popup pages. Take the specs out of the popup and add them to the guitar page, but slightly smaller font.
Don't worry so much about whitespace, its the flow your looking for here in your pages.
What about a form for interaction between a prospective customer? You could add it to your Contact Us page before or after the email.
If you would like I could help you out, PM me. BTW what software are you using to design the page?
Jeff