Date calcs and beyond

I am starting to get into a situation where I am going to have to get
totals for the past 12 months and have started playing with code. Here
is where I am at:

  def self.tm_beg
    Time.now.beginning_of_month
  end

  def tm_end
    Time.now.end_of_month
  end

  def tm_beg_less_1
    tm_beg.last_month.beginning_of_month
  end

  def tm_end_less_1
    tm_end.last_month.end_of_month
  end

and so on to tm_beg_less_11/tm_end_less_11

My intention is to use it something like this in the personnel.rb
model...
@clinical_supervisions_tm = ClinicalReview.find(:all,
   :conditions => ["personnel_id = ? AND
    supv_date BETWEEN tm_beg .. tm_end", self.id])
NOTE: don't worry about syntax because I will use ez-where to handle the
search

This seems to work fine in console so my questions are:

- Am I missing a plugin that does this for me? (the date math for 12
months)

- If I put these calcs in lib/t_calcs.rb or application.rb or
application_helper.rb, it seems not to matter because I am going to have
to call it via Class anyway, is there a preferred way?

- Does someone have the whole enchilada calendar utilities/engine that
will make me stop hating date/time calcs (not that I don't love the
utility that rails gives me for free)?

Thanks

Craig