How to solve this with Stored Procedure.

I have Enter for holiday Details like this below my Table Struture


Table Stru
===========
Days varcahr
DFrom Datetime
DTo Datetime


here my issue i will enter from date to date to insert
my intension

1.How to Restrict Duplicate Date Insert in sql
2. How to restrict between date already give the holdays date
ex:From Date ->25/11/2011-DD/MM/yyyy Todate like this->27/11/2011-DD/MM/yyyy format
here user enter suppose -26/11/2011 but this is not allow here becos already leave date alloted so
how will do this one stored proceduere any one post this i need most urgent .

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