Question : how to get authorized certificate for two domains for SBS 2008?

Hello,

I have purchased an authorized certificate for my server but they issued for this domain only:

remote.mydomain.com

My question is how about autodiscover.mydomain.com because my users don't know how to install the self signed certificate.

Answer : how to get authorized certificate for two domains for SBS 2008?

in the certificate request you can add the SAN.
usually when you buy a  public certificate (eg by DigiCert), you can enter up to 5 SAN.
The SAN (Subject Alternative Name) are used to add other names to which the certificate is authentic (in your case for autodiscovery).
Use the Exchange wizard to create a certificate, this will include all the names useful for creating the right cert req.