SQL SERVER 2000 QUERY CONVERSION

I have a query written in sql server 2000 and I want to re-write that to use in sql server 2005 and newer versions. here is the query:

IF @AgrpID > 0 SELECT @Sql = @Sql + ' AND C.AGRP_ID = ' + CONVERT(VarChar(10), @AgrpID)

P.S: COM.DBO.CNTL_ContactCenterLeads C I dont undrestant what is the

SELECT @Sql = @Sql + ' AND C.AGRP_ID = ' + CONVERT(VarChar(10), @AgrpID)

does, and if I have a #temp table replace with @sql, how can I re-write this query with the same logic.