Two separate login lists

Hi all, I have just updated our site which now features a store and a login area for clients. However anyone who enters details for the store, also get access to the login area for clients as it shares the same details.
How do I separate the two?
I would also like to pre sign up the client area email and passwords and then limit it to these addresses without people being able to sign up, only sign in with the details I created for them.
Can I do this?

TIA.