Need a SQL Server command for instr

I need a command in SQL Server 2000 that already exist in Oracle. The Oracle command is INSTR, It returns the number of spaces from the left a specific character is in a string. If you wanted to find the location of the third ‘i’ in the word Mississippi you would type instr(‘mississippi’,i,3,1) and it would return 8. I tried to use this command in SQL SErver 2000 and it says the instr is an invalid argument.