in datasheet view, the initial order is set by the order in which fields are selected in the underlying query. If you subsequently add additional fields, they will be added in columns to the right. So far as I know there is no easy way other than deleting all the columns in design view and then selecting them again.
You might try a bit of code - something along the lines of this untested code in the form load event
Code:
dim I as integer
dim fld as field
for I=0 to me.recordset.fields.count-1
me.recordset.fields(I).columnorder=i
next i