They will always be treated as a literal unless used in wilcard searching with LIKE and PATINDEX in which case you need to 'ESCAPE' them, ie
LIKE '%[%]%'
LIKE '%[_]%'
or
LIKE '%\%%' ESCAPE '\'
LIKE '%\_%' ESCAPE '\'
or
PATINDEX('%[%]%',column)
PATINDEX('%[_]%',column)
Look up "Pattern Matching in Search Conditions" on BOL for more info
Far away is close at hand in the images of elsewhere.
Anon.