>   >  
>   
> - puts  
> + rows = []
> + puts "Tables_in_valutation"
> + res.each {|x| p x.to_s; rows<<x}
>  
You can take this one step further to actually print a table with
hirb, http://github.com/cldwalker/hirb:

require "mysql"
dbh = Mysql.real_connect("localhost", "root", "******", "valuation")
res = dbh.query("show tables")
rows = []
res.each {|e| rows << e }
puts Hirb::Helpers::AutoTable.render(rows, :headers=>["Tables in
valuation"])

With my own database this produces:
+---------------------+
| Tables in valuation |
+---------------------+
| nodes               |
| schema_migrations   |
| taggings            |
| tags                |
| trees               |
| urls                |
+---------------------+
6 rows in set

If you're interested in having irb act as a database shell, try hirb
with one of
the database gems listed in http://tagaholic.me/2010/03/11/hirb-and-tables-for-all.html

Gabriel