Excel 2007 : Average every nth group of rows into new column

Hello all:

I currently have data that is displayed in seconds, yet displaying any graphs with these points that go up to 4 hours is impossible. Therefore, I'm trying to get an average of every 60 points that are in one column and display them in another column (and worksheet) as the average and thus reduces my points / 60.

Ex.

Time (s) Data
1 xx
2 xx
3.. xx
60 yy
61 yy
62... yy
120... zz

and turn this into

Time(min) Data
1 sum(xx)/60
2 sum (yy)/60
3 sum (zz)/60

in another column (and worksheet).

Any help? I've looked at Average every nth row but that only give the average of row entries 5,10, 15...etc.. I'm looking for the average of each 5 to be displayed consecutively.

Thanks in advance