I believe you have to declare it as variable number in stead - so it will be
VB Code:
  1. mysht.columns(13).numberformat ="#.##"
I you wan't to put in 1,000 separators, then you can do like this #,#,#.## for instance.

Try experimenting using the format cells --> custom in your worksheet - it should give you a clue of what you can do...