Stored Procedure should not enter same name with diff id...HELP

[Riaaaa]

Hi frdz,

I have created the form for entering the company details with its general information in asp.net C# 2005.

I want to put the validation that the user cannot enter the same name of company's twice with the different id's.

I have created the stored procedure for the insert and update :

The following is the insert stored procedure created in the SQL SERVER 2005.

 
if exists (Select companyname from companymaster where companyname =@companyname)
        Print 'CompanyName already exists'
      IF NOT EXISTS( SELECT companyname FROM companymaster WHERE companyname <> @companyname and companyid <> @companyid)
    BEGIN
        INSERT INTO companymaster
                          (companyname, address1,address2,abbrecomp)
        VALUES     (@companyname,@address1,@address2,@abbrecomp)
        SELECT @companyid = SCOPE_IDENTITY()
 
 

The stored procedure is running but inspite of checking that companyname is not equal to companyname it allows me to add the companyname with the same name again creating the identity of the companyid.

I want to execute this stored procedure for my asp.net C# 2005.

Can i use trigger for the insert of the companyname with same name existing check ??

If yes,then can anyone tell me how to write the trigger for the above insert tabel of the insert query.
Or else just tell me what should be modified for the stored procedure code...

Thanxs in adv.