want to know if any validation exists

[soumya jyoti guru]

Hi all,
        I  am facing a problem while validating two dates used in the
same form (start date, end date).I have written a code
for create and there I had included two fields named as start date and
end date.
       The problem is that the data gets created even if the start
date=2010-09-30 and the end date=2010-09-01 which changes the meaning
of the two fields.Can anybody suggest me a way to show a error
message while this is done.
with regards
Soumya