Are you just going to run a script saying, show me all users within last X days/weeks/month?
Do you mean "last week" as in 7 days ago, or the last Sunday-Sat? Are these all going to be on one page? Some people could be duplicated as they were signed up both last week and last month... and many people could be for both last month and last week, 2 weeks, etc. What should you do with duplicates?