Have a counter table with a row for each day containing a hit count. I use the date in form YYYYMMDD as a key, and a simple int as the counter. For each hit, just find the current date and increment the bucket. Each night, add all days older than 7 days to bucket '00000000'.

So for "visits this week" you'd use:

select sum(counter) from hit_counts where hit_date > dateadd(d,-7,getdate())

and for "visits all time":

select sum(counter) from hit_counts

Note: I've used Sybase/MS SQL Sever syntax here, may vary for other DB servers....

...roboticus