Hello,
For the time being TeamCity does not provide dedicated functionality to address this case. You can file a request into our issue tracker so that we can see how many votes it will get. Please also describe your case/workflow in more detail so that we can understand the underlying requirements.
As to current workarounds, it seems that the only possible way is to detect the event from outside of TeamCIty and trigger the necessary build (e.g. with HTTP GET request). The triggerer can also provide the name of the label.
And the build should then retrieve the sources from CVS as part of the build script, since TeamCity can only get sources for the fixed VCS root settings.
Here is also a related issue in our tracker.
Another option may be to try to integrate the release management tool into TeamCity and instead of watching new tag creation, try to wrap the activity inside TeamCity. Possibility to do this this greately depends on your workflow.
--
Best regards,
Yegor Yarko
Project Manager (TeamCity)
JetBrains, Inc
http://www.jetbrains.com
"Develop with pleasure!"