Let us suppose we wish to randomly sample n cases of data comprising N people.
1. Put =RAND()*N in row 1 of the column adjacent to the right most data column in the spreadsheet
2. Copy and paste into remaining N-1 rows
3. Go to Data>sort on the EXCEL menu and make sure you sort in ascending order by the column you have just created. Click OK.
4. Delete rows n+1 to N.
We have randomly permuted the data rows so that the first, or any adjacent, n rows represent a random sample of size n.
Block randomization and other procedures may also be done on-line here.