using wildcards in place of hostname

[steve.anon at gmail.com]

Apologies for the newbie question.

Is it possible to have *.domain.com pointing a specific Ip address.
That is, no matter what the hostname for the domain will be, the user
will be directed there?

I'm asking because I'm working on something similar to blogger.com.
Users sign up and they get their own webpage, with a domain name of
'username.blogger.com'.

blogger.com is doing it on the fly (as you sign up, immediately with no
propagation time). Anyone has any clue on how they do that?

Cheers,

Steve