After fixing up the site's coding, I've confirmed that most of the site (meaning its layout and the major pages) works well in all major browsers.

Tested:
Internet Explorer 8: No flaws
Internet Explorer 7: No flaws
Internet Explorer 6: Small overlap (correcting now), transparency
Internet Explorer 5.5: Small right margin (correcting now), transparency
Internet Explorer 3: Too terrible to list
Firefox 3.5: No flaws
Firefox 3: No flaws
Firefox 2: No flaws
Firefox 1.5: Small graphics issues
Safari 4: Hit counter shows error (alleviated on home page)
Chrome 3: No flaws
Opera 9.36: No flaws
Opera Wii: YouTube player JavaScript doesn't work
Netscape 9: Small graphics issues
Netscape 4.8: Too terrible to list
Konqueror: Hit counter shows error

Untested in last month:
Opera 10
Safari 3
Safari 2
Opera DSi
iPhone

There is also an issue where some browsers show anything in Arial Black in italics. I'm fixing that now too.

Oh good, so the all of 3 people in the world who are using web browsers over 5 years old and actually use that as their main browser for this particular website will be able to enjoy it.

About 10% of visitors have IE6 or FF1.5, so it's still important to deal with that.

IE3? All Microsoft OS's above 95 has 4 onwards... And people still use FF1.5? 0_o

IE3 still runs on Vista, so I just tested it (and Netscape 4.8 ) as a joke. As for browsers, here is a general breakdown (for October 2009). I consider anything 0.1% and above as significant because of the large number of monthly page views. All unlisted browsers have numbers too low to be of significance.
Internet Explorer
IE8: 38.7%
IE7: 11.9%
IE6: 2.8%
IE5.5: 0.1%
Firefox
FF3.5: 20.5%
FF3.0: 8.2%
FF2.0: 0.2%
FF1.5: 5.3% (SERIOUSLY?!)
Netscape
NS5: 0.2%
"Other"
Chrome: 4.6%
Safari: 2.9%
Opera: 2.1%
"Mozilla": 0.2%