It is not necessary to install the base code, you can install the latest fixpack directly and then apply the license from your base code package (use db2licm program).
Here is the link to fixpacks:
IBM - DB2 Fix Packs by version for DB2 for Linux, UNIX and Windows
However, 9.7.3 server has been withdrawn due to some Hiper APARs. There probably will be a 9.7.3a fix in a few weeks, or just get the 9.7.2 for now.
One reason that it is better to install the latest fixpack first (instead of base code and then upgrade with fixpack) is that there are sometimes problems with the install code in the initial release (such as 9.7.0). I definitely would not create a database with 9.7.0.
Note that if you want DB2 Express-C, that is located elsewhere, and you cannot install fixpacks to it (must just install latest Express-C code).
M. A. Feldman
IBM Certified DBA on DB2 for Linux, UNIX, and Windows
IBM Certified DBA on DB2 for z/OS and OS/390