If your after a timestamp for when a model is created, just include a created_at column in your table of DateTime. Rails will automatically stamp it when it gets created.
Also if your after an update timestamp there is similar functionality from a field updated_at again type DateTime
If you want to convert a text input to a date, you could use
params[:my_date_field].to_time (or to_date)
There is a plugin on www.agilewebdevelopment.com for dates. Maybe you would have some luck with that.
Or alternatively there is a project called chronic that may be helpful.
Its very early but looks promising
Hope that gets you started…