If your problem is that you put a new .jar in Alfresco/web-inf/lib/ and Alfresco doesn´t read it, I´ll sugest a little solution:
1) Pick an existing jar file from alfresco and make a copy.
2) Use winrar and insert your clases into the copied jar.
3) Delete the original Alfresco´s files from the copied jar.
4) rename it and move the jar file to Alfresco/web-inf/lib/.
I know that its a bit extrange solution, but it worked for me when I had the same problem.
I hope this will help you.