Exactly. OS detection is done at execution.

It does detect the OS on execution.

Additionally, in the interim, you can use the NoDriveTypeAutoRun key to adjust how Autorun reacts. http://www.microsoft.com/technet/prodtechnol/windows2000serv/reskit/regentry/93502.mspx?mfr=true 0x4 is the bit you are after. More information is here: http://support.microsoft.com/kb/953252 I'll recommend this to the Fix it team and we'll see what happens.

Send e-mail to fixit4me@microsoft.com with your automation recommendation. The team will analyze the request, attempt to understand all of the scenarios, and post a Fix it package.