I have a sony xplod 1652z 1000 watt amp and want to hook up 2 subs and the speakers that are already installed in the truck is that possible?

It is possible, just as long as you maintain the resistance within the acceptable ranges, and so long as the speakers are able to handle the power. Also, make sure that both channels have the same number of speakers and resistance on each channel. You should be safe that way.
I've had a few people hook up multiple speakers up to the same amp, and basically you could hook up an indefinite number of speakers to one amp, so long as the resistance remains in that range. However, you will loose power to each individual speaker, and therefore, your system will start to loose volume with each added speaker.
The different style of circuits you can use are parallel and series circuits, the resistance formulas for each can be found easily online. Just ensure that each circuit is properly attached and calculated, and you should have a nice amplified system.
Again, in order to not fry the amp, ensure that both channels have the same resistance, and that they are within the appropriate ranges. It is possible, just as long as you maintain the resistance within the acceptable ranges, and so long as the speakers are able to handle the power. Also, make sure that both channels have the same number of speakers and resistance on each channel. You should be safe that way. I've had a few people hook up multiple speakers up to the same amp, and basically you could hook up an indefinite number of speakers to one amp, so long as the resistance remains in that range. However, you will loose power to each individual speaker, and therefore, your system will start to loose volume with each added speaker. The different style of circuits you can use are parallel and series circuits, the resistance formulas for each can be found easily online. Just ensure that each circuit is properly attached and calculated, and you should have a nice amplified system. Again, in order to not fry the amp, ensure that both channels have the same resistance, and that they are within the appropriate ranges.