min and max values w/in specific date range

Hi,

I have a table of dates and values and would very much like to know a formula for returning the min and mean values for each column within a specified time (date) period.

Table is as follows

Date value(a) Value (b) ....
1/1/09 10 8
2/1/09 8 6
3/1/09 5 2

Thanks in advance!!