I think that your copy of Tiles was compiled under
Java 5 and you're attempting to run it in a java 1.4 environment.
Java 1.4 is long since past end-of-life and even Java 5 should be receeding in the rear-view mirror at this point. For that matter, it wouldn't be a bad idea to move to
Tomcat 6, since Tomcat 7 is probably going to go into production between too much longer.
Getting too far behind the curve doesn't save anything. While it's true that Java - unlike certain other platforms I could mention - doesn't force you into panic upgrades, you're not going to find too much support once things get really ancient, and you're also putting yourself at risk because older releases have security issues that newer releases have repaired. Plus Tomcat continues to get better performance with each new release.
It's a lot easier to fix a "jdbc driver not fond" problem than a class version issue, so that should be an indication right there as to the best approach. You just need to find a suitable JDBC driver and put it in the proper Tomcat library directory. I think it's server/lib, but I haven't run Tomcat 5 in probably 4 years now so I no longer remember. Tomcat6 doesn't require 3 separate library directories like earlier Tomcats did.