How can I list only the customers who registered during my sale week?

Use the registration date filter on the customer list.

1. Go to Customers → Manage Customers.
2. Pick a date in Registered from and another in Registered to. The list updates as soon as you choose a date, and both days are included.
3. Leave one end empty if you want "since" or "up to" a date.

You can combine the dates with the Search customers… box. The filter is saved in the page address, so you can bookmark or share the filtered view. The total for the range shows in the pagination under the list.