VSS Backup

Hi,

I intend to write an application which would be used by third party backup
applications to freeze Exchange/SQL before taking a backup. Once the backup is
complete then the third party backup application will call the unfreeze api from
our app that will resume exchange/sql. We intend to do the above using VSS. Can
anyone please shed some light on the same.
Also can anyone please provide me the link to VSS SDK Documentation. I am unable
to get it. I have VSS SDK 7.2.
If this is not the correct site for this post kindly let me know which is the
correct one in case you know.

Thanks,
Deena
Note: I had posted this query initially on NTFSD, but was guided that it would be appropriate to post it here. So reposting it.