Microsoft supports event  handling through the object model at the
site level for deletion, but not for creation.

There is a workaround, apparently, that uses Features to achieve the same
result. Start with this article.

msdn.microsoft.com/en-us/library/ms463479.aspx

I haven't actually tried this, but it looks interesting. Please let us know
how you get on with it.

There is no specific event  that will fire  when a web site  is added to a site
collection. The workaround I normally use is to create a WEB scoped Feature
Receiver and then set that Feature to be auto activated by stapling it to the
site definition using a Feature Site Template Association. When a new web site
is created using that site definition the Feature will be activated and the
Feature Activated method of the Feature Receiver will be raised. If you want
this to happen only for a specific  site collection  you would need to add code
that would check which site collection had raised the event and either respond
or exit without action.