The first calendar below uses td:first-of-type, td:last-of-type {display:none} to hide the Sunday and Saturday portion of the calendar:

 

5-day week calendar
S M T W Th F Sat
      1 2 3 4
5 6 7 8 9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30 31  
7-day week calendar
S M T W Th F Sat
      1 2 3 4
5 6 7 8 9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30 31