Nadya,
There is no easier way than using the product that way it was designed. DateTime is the data type for storing date and time. You can modify the function to use a data plus the time as a string.;
lcDate = DTOS(TheDateField)
ltDateTime = EVAL("{^"+LEFT(lcDate,4)+;
"/"+SUBSTR(lcDate,5,2)+;
"/"+RIGHT(lcDate,2)+" "+;
lcTime+"}")
Now put that in a datetime field and you're done.