I want to programmatically (e.g., from a script, console mode program,
or Windows program) change the link speed of an Ethernet interface in
a WindowsXP PC.  Rebooting is not acceptable.  I have tried to do this
via SNMP and it does not seem to work.  My SNMP incantations are:

c:\work>snmptool get 127.0.0.1 public interfaces.ifTable.ifEntry.ifDescr.2
  ErrorStatus: 0 (No Error)
   ErrorIndex: 0
    varbind 1:
         Name: interfaces.ifTable.ifEntry.ifDescr.2
          OID: 1.3.6.1.2.1.2.2.1.2.2
         Type: OCTET STRING
       Length: 68
        Value: Intel(R) PRO/1000 MT Network Connection - Packet Scheduler Miniport

c:\work>snmptool get 127.0.0.1 public interfaces.ifTable.ifEntry.ifSpeed.2
  ErrorStatus: 0 (No Error)
   ErrorIndex: 0
    varbind 1:
         Name: interfaces.ifTable.ifEntry.ifSpeed.2
          OID: 1.3.6.1.2.1.2.2.1.5.2
         Type: Gauge
        Value: 100000000

c:\work>snmptool set 127.0.0.1 public
interfaces.ifTable.ifEntry.ifSpeed.2 6 10000000
  ErrorStatus: 2 (No such variable name)
   ErrorIndex: 1
    varbind 1:
         Name: interfaces.ifTable.ifEntry.ifSpeed.2
          OID: 1.3.6.1.2.1.2.2.1.5.2
         Type: Gauge
        Value: 10000000

Yes, I have made public READWRITE.  

I can change my link speed (and without reboot) from the properties
dialog box for my NIC.  So, clearly (?!) there must be a way for me to
do this from a program.

Five stars to someone who can show me how to do this with an example
program.  Preferred is to get SNMP to work.  Second preference is
within a C language program.  If the solution must be NIC specific, I
can live with that (but, a general solution is preferred).

Thanks!