tomcat and jdbc

[e.chan]

Hi
I am using tomcat in a win 98 environment.
I registered my db as an ODBC data source.
I have tried to go to the tomcat conf file looking for server.xml
To enable the jdbc realm to be loaded but 
Tomcat is not connecting to jdbc.
Please help... I have checkd with friends with same settings as I have -
theirs work and mine doesn’t...

Can you point me in the right direction plse. 
liz