Express-C was not available in DB2 7.1
As a general rule of thumb, a DB2 Client can connect to a DB2 Servers two versions prior and one version after. Using this rule, DB2 9.7 should be able to connect to DB2 7.1 , but there is no gurantee it can or it will.
ftp://ftp.software.ibm.com/
Dig into the directories and there is a possibility you find DB2 7.1 or DB2 8.x. The likelihood of DB2 8.x being able to connect to 7.1 is higher.
HTH