1) Install the OS language. This can be done through the Control Panel.
2) Download Your Specific SharePoint Server 2007 Language Pack . Navigate to http://www.microsoft.com/downloads/details.aspx?FamilyID=2447426b-8689-4768-bff0-cbb511599a45 and select your language.
3) Install the above language pack
4) Re-run the configuration wizard of SharePoint again. A folder of the "locale" e.g. 2052 would be created in the TEMPLATE folder.
5) When creating a new Top Level site, a drop down of the languages would be populated and the language could be selected.
Note - The above steps are not in detail.