Multistore on PS 1.7.x - share customers, subdomains etc.

[magisterson]

Hi all,

I need to create multisore on one web domain, for example www.mystore.com - there will be two stores:

1. normal products that everyone can buy using normal money transfers, placed on subdomain: shop.mystore.com
2. second store on another subdomain: catalog.mystore.com, and this store will offer only bonus products that customers can buy using loyalty points earned in first store.

My questions:

a) Can I make it on subdomains or I need to place stores on catalogs like: mystore.com/shop & mystore.com/catalog?
b) Can I share customers in theese two stores? I need to have functionality that let users to create account only one time. One accounts for two shops: products shop, and points/catalog shop.

Thanks!