To compare 2 airplanes from 2 different manufacturers you should establish a criteria, i.e. range, pasenger capacity, or MTOW. The passenger capacity, however is much dependent on the airline's configuration and can vary greatly on the same aircraft. (JAL's 744Ds can hold up to 568 people compared to about 400 on standard 3-class configuration).
To make a fair comparisson you should concentrated on competing models with similar range/capacity that are usually used on similar routes. It will be fair to say that the A330-300 competes with 777-200A (not-ER model), while the A330-200 competes with the 767-400ER/ERX. A smaller derivative, the A 330-500 would compete with the 767-300ER/ERX.
If you are interested in numbers, you can find them on either manufacturer's site.