Need To Count Rows Within A Timespan

I'm new to MS SQL having used MySQL for several years now. I just can't figure out the syntax on counting or selecting rows

a) in the Last X (days, weeks, months...)

or

b) between "date X" and "date Y"

I've tried this to get the last week:
SELECT COUNT(*)
FROM contacts
WHERE CONVERT(datetime,timestamp) < (GETDATE() - DATEADD(DAY,7,GETDATE()))
...but I always get a total that includes rows outside the span.

Any suggestions? Thanks!