Join Date: Jan 2008
Without a better picture of the nut, I cannot be sure, but it appears to be a CGA320 nut.
You will need to find a paintball to CGA320 adapter (can be easily found online). The adapter will depress the pin down and allow gas to flow into the regulator.
Without more information regarding the regulator, I cannot give any details, but I assume you checked and ensured the regulator's working pressures are suitable.
Similarly, since we usually operate from 10-30 PSI or so, if the low pressure gauge's lowest value is (say) 100 PSI, it will be quite difficult to use.
Finally, you will need to replace the output side on the regulator (at the very least, you will need a needle/metering valve).
I would recommend you use a solenoid in addition to the needle valve, so that you can control your CO2 via a timer.
For more information regarding the parts required for pressurized CO2, please take a look at my pressurized CO2 guide (linked in my signature).
Edit: One last thing, you will want to somehow secure/strap down that paintball canister when it is in use, because it will certainly be top heavy with the regulator. As I'm sure you already know, you cannot use the cylinder on its side.