How do I save an expandable event log of an expandable size?

I was thinking about writing a simple "event log" that takes a list of parameters and stores the event messages in a log file, the problem is that I see this file getting quite large (say 1M records or more) question How can I implement this system without pulling my teeth, I know that SQL will be a possible way.

XML would be perfect, but not very practical for scalability if I don't go blank.

Example of logging

----- Time Date -------- --------- Sender ---------------------- - - ------- Tags ---------- - Message ----------

12/24/2008 24:00:00 $ DOMAIN \ SYSTEM \ Application $: Trivial :: Notification: Christmas in 1 sec