Time.parse("2010-01-01 12:30:00").getutc
EDIT
(grinding teeth while thinking about the nightmare which is Ruby/Rails date/time handling)
OK, how about this:
Time.zone.parse("2010-01-01 12:30:00").utc
Note that Time.zone.parse returns a DateTime, while appending the .utc gives you a Time. There are differences, so beware.
Also, Time.zone is part of Rails (ActiveSupport), not Ruby. Just so you know.