Answer:
You cant woohoo on the PlayStation 2 version. They just get in the bed and relax. While they relax all they do is read a book. If your not relaxing then you can only sleep but I believe on the Sims 2 you can woohoo.
if you are talking about making the pets woohoo then all you have to do is go to your pet and say try offspring with ... whatever pets there are when the options for try offspring with are (note: you need like a pet house, you can buy them in buy mode)