Self Employed/Working Part Time

Hi there.

I'm looking to take the plunge into running my own Freelance business. But before i dive in head-first, I want to build it up slowly.

I read that in order to start your own business, you have to contact the Inland Revenue and declare yourself self-employed. But if i want to a=start my own buisness AND continue working part time at my local retail store, do i still have to tell them i'm self employed?

Also, does anyone know the first steps to getting off the ground with the business, in terms of any books or free booklets or who i would go and see about it? :eyes

Thanks