Datetime: convert and subtract?

[titanotam]

I have some problem with my project.
1) I want to convert String (ex : "14/03/1987",...) to system datetime
2) I want this function : Subtract(date1,date2)
==> result: if subtract(date1, date2) > "1 month" then ......do something
else if .........do something
Please help me.
Thanks a lot.