Well, I use 2048x1536 - but that isn't the issue. Anyone with a browser bigger than 800x600 will see it differently.
In your tables, look at the tags. You have:
<table border="0" cellpadding="0" cellspacing="0"
width="80%" style="border-collapse: collapse;">
That makes it 80% of the users browser window no matter what size they have.
Change that bit to
width="760" (for example) and the table will always be 760 pixels wide.
Make sure you do it to all tables as necessary, and make sure you get the numbers right in nested tables else you'll have fun :)
As for design - take a look at some competitors:
http://www.musicmatch.com/ (click their 'get it now' button)
http://www.audioactive.com/download/ (look at their 'tech talk' button - this is a bit OTT but you see how their sites are a bit more expanded)