Nevermind. My company had pushed a group policy to force all intranet sites to compatibility mode which is causing nagiosgraph's web interface to break.
OK, I was able to solve this. Here is the problem and my solution for anyone else who encounters this.
Solution: According to this page at MSDN (http://social.msdn.microsoft.com/Forums/en-US/iewebdevelopment/thread/acf1e236-715b-4feb-8132-f88e8b6652c5) one can force IE8 to use standards mode when the header "X-UA-Compatible" is sent with a value of "IE=8".
I fixed this for Nagiosgraph by modifying the ngshared.pm module. Find the "printheader" subroutine, which was on line 2505 in my file. The second command in the subroutine is:
my $rval = $cgi->header;
Change it to the following:
my $rval = $cgi->header('-X-UA-Compatible'=>'IE=8');
The CGI programs will then display fine in IE8 while leaving all your other intranet sites in compatibility mode.