Accessing system environment variables in Windows Server 2003 / IIS 6

We're using the Verisign PayFlowPRO component to validate credit cards
and that component requires an environment variable to find it's
certificate.

I've set the system variable up (right-click My Computer, Advanced,
Environment Variables, etc.) and verified (using the "set" command)
that it exists, but if I dump the environment variables using the
following code not all of the system variables show up.

Here's the code I'm using to dump the environment variables:

<script language="C#" runat="server">
void Page_Load(Object s, EventArgs e) {
Response.Write(Environment.MachineName + "<p>");
IDictionaryEnumerator iter =
Environment.GetEnvironmentVariables().GetEnumerator();
while ( iter.MoveNext() ) {
Response.Write (iter.Key + ": " + iter.Value + "<br>");
}
}
</script>


Here's the output:

TT-WEB01T

SystemDrive: C:
USERPROFILE: C:\Documents and Settings\LocalService
Path: C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem
ClusterLog: C:\WINDOWS\Cluster\cluster.log
CommonProgramFiles: C:\Program Files\Common Files
ProgramFiles: C:\Program Files
NUMBER_OF_PROCESSORS: 1
TEMP: C:\WINDOWS\TEMP
TMP: C:\WINDOWS\TEMP
ComSpec: C:\WINDOWS\system32\cmd.exe
PROCESSOR_IDENTIFIER: x86 Family 6 Model 11 Stepping 1, GenuineIntel
COMPUTERNAME: TT-WEB01T
PROCESSOR_LEVEL: 6
OS: Windows_NT
SystemRoot: C:\WINDOWS
windir: C:\WINDOWS
APP_POOL_ID: DefaultAppPool
ALLUSERSPROFILE: C:\Documents and Settings\All Users
PATHEXT: .COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH
PROCESSOR_ARCHITECTURE: x86
PROCESSOR_REVISION: 0b01

When I run the "set" command from that server I get the following
output:
C:\>set
ALLUSERSPROFILE=C:\Documents and Settings\All Users
APPDATA=C:\Documents and Settings\scott.frazer\Application Data
CLIENTNAME=SFRAZER-LT
ClusterLog=C:\WINDOWS\Cluster\cluster.log
CommonProgramFiles=C:\Program Files\Common Files
COMPUTERNAME=TT-WEB01T
ComSpec=C:\WINDOWS\system32\cmd.exe
HOMEDRIVE=C:
HOMEPATH=\Documents and Settings\scott.frazer
LOGONSERVER=\\MT-DC01
NUMBER_OF_PROCESSORS=1
OS=Windows_NT
Path=C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem
PATHEXT=.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH
PFPRO_CERT_PATH=c:\Verisign\payflowpro\win32\certs
PROCESSOR_ARCHITECTURE=x86
PROCESSOR_IDENTIFIER=x86 Family 6 Model 11 Stepping 1, GenuineIntel
PROCESSOR_LEVEL=6
PROCESSOR_REVISION=0b01
ProgramFiles=C:\Program Files
PROMPT=$P$G
SESSIONNAME=RDP-Tcp#9
SystemDrive=C:
SystemRoot=C:\WINDOWS
TEMP=C:\DOCUME~1\SCOTT~1.FRA\LOCALS~1\Temp\1
TMP=C:\DOCUME~1\SCOTT~1.FRA\LOCALS~1\Temp\1
USERDNSDOMAIN=<omitted>
USERDOMAIN=<omitted>
USERNAME=scott.frazer
USERPROFILE=C:\Documents and Settings\scott.frazer
windir=C:\WINDOWS

Thanks in advance.