I think you still have to worry about IE 6, 7 and 8, as well as Firefox 2 & 3, Safari and now Chrome.
Coley, it opened up fine in my IE 7 right off the bat. If you're concerned, another option is to make the buttons into one single graphic and then map the link zones.
Also, there's a good site for checking cross-browser compatibility:
www.anybrowser.com
I know how to use CSS but I have to admit I still use a lot of tables.

It's just so much easier in some instances and I'm convinced future browsers will always support them...