I asked the same thing on the MS sharepoint services news groups and got
this url as a response, seems to do answer the question and im gonna try it
out today on our test sps/wss server

weblogs.asp.net/jan/archive/2004/03/27/97335.aspx

Another way to do this (and i'm not sure how "good" a way it is) is
simply to make distribution lists in Exchange and set  the alert  to that
distribution list, I think we have a half dozen or so of those using
public folders in Exchange which are simple to setup. This way you can
add and subtract users on the list in exchange and not hassle with the
sharepoint end. It's pretty simple to manage and we've done it for
multiple offices and web-form submissions and so forth...

not thought of that way, but I don't have AD yet so maybe that's
why

Perhaps this may be helpful as well:

"A web part that allows admins to set  up alerts  for other users"

weblogs.asp.net/jan/archive/2004/03/27/97335.aspx

I just wanted to add that I've been using the web part that Noel listed
below for many months and it works very well for what we need. Just one
warning, I found that once you add it to the page so that you can add
your users, make sure you do not hide it from the page. Your users will
not be able to login. I found out the hard way. So you would need to
remove it from the page once you are finished.