Transaction Trouble

I'm having trouble using transactions in my Delphi app.
I've created a database and want to maintain integrity between two tables when
updating i.e. if I store in one I want to store on the the other, if one fails
I want to back out the successful update.

I've placed a TDatabase component in a data module,  set the alias to my
database name alias but when I try to connect I get an 'Object not found'
error. Any help gratefuly received as I'm tearing out what's left of my hair !

Thanks in advance