despite the fact that gem option is switched on at this repo, gem technoweenie-acts_as_versioned cannot be found :(

Steps to reproduce:
Create a new Rails app with a single model named "bill.rb" with acts_as_versioned .
Set config/database.yml to use MySQL
Generate a migration called "create_bills".
In this migration, create a table named "bill" with a single attribute named "amount" with a "decimal" datatype. Include the "Bill.create_versioned_table" line.
Try "rake db:migrate" (db:drop & db:create as needed).
Note: No integer type has byte size 10 rake aborted! error
Add a specification of :scale => 2 to the migration datatype specification. The error remains.
Add a specification of :precision => 8 (even without :scale). The error disappears.

Tested on OSX 10.5.8, Ruby 1.8.6, Rails 2.3.3, acts_as_versioned 0.2.3

On running the following migrations:

class AddVersionToPost < ActiveRecord::Migration
  def self.up
    Post.create_versioned_table
  end

  def self.down
    Post.drop_versioned_table
  end
end

and where Post is:

class Post
  acts_as_versioned
end