I have a AMD p7-1240, is that even possible to mine with nowadays?
That's a "HP P7-1240" powered by an AMD APU, not an "AMD P7-1240", I presume.
It should be possible to use it as the basis for a mining system, the CPU is a bit overkill for supporting extra GPUs with (I've got 2 machines with the A10 5700 in them) but it should work.
It's not going to be a REAL good CPU miner, even if you don't use the GPU side to mine on at all - I think I was seeing about 70 hash/sec on one of mine on XMR.
GPU side of the APU can mine some stuff, but it's very poor at it - ballpark 10-12 hash/sec on ZEC for example - biggest issues there are (1) not GCN (2) DDR3 RAM
About the only thing even close to mining-related that GPU is good at is RC5 work via the MooWrapper project (which can earn some Gridcoin).
Add some "real" GPUs though and the system should work well enough - just watch your power supply limits, HP (like Dell) tends to put PS in their units with "just enough power" to support the maximum configuration THEY sold the unit as, so you will likely have to upgrade the PS if you add more than one mid-level GPU to the machine.
