Haha. 45lbs is by no means light enough for a DH bike.
If you'd like to post up specs it'd be helpful.
The best place to start is rotational weight as this is the part that will effect your riding most. It will also give you the best $/G ratio.
A good combo is Hope Pro 2 on a Mavic EX721. The 721 is a very strong rim but really light too, and the Pro 2 is just unbeatable for performance/weight/price.
Then tyres and tubes are usually a good place to go to as well. A lot of people are now running XC tubes with a Dual Ply tyre. Then you can start looking at suspension, cranks, and brakes.