I would just put the enlarger on a solid table. If you follow cjbecker's advice and just wait for any vibrations to calm down it should be fine for most circumstances. I personally would opt for a solid desk before using a fridge. When a fridge is on there is a little motor in it that will run and cause vibrations.

nickj, I am not sure where you live but in the US most domestic walls have a solid wood skeleton behind the sheet rock. When hanging things on the wall you should use a stud finder and nail or screw through the drywall and into a wood stud. I will sometimes hang light picture frames just into the drywall but anything else will require more substantial anchoring. It doesn't have to be bolted into concrete though.