Well, It depends on a lot of things. The obvious thing to do with 20K would be to buy a ps3 but then can you afford to get games worth 2K every now and then? If you can, that's the best thing to do.
Now, Do you have Full HD television with you. Unless you do, buying a PS3 is not justified at all.
A PS3 can provide close if not better visuals than an average PC if on an HD display, non HD... not much difference.
If you are planing on upgrading your PC, You should be more concerned with you graphics card than your processor/Mobo. You should get a good enough card to be able to run all latest games at a good setting. Lets calculate
You have a p4 processor, I would suggest you get at least a dual core processor to get decent performance.
You can very easily get a dual core processor and a compatible MOBO for 10,000 and with the rest you could buy a GTX 460. You would be able to get a good enough performance out of this machine.
Then too it all matters, Do you play in HD? If you do, this would only provide minimum quality where again the PS3 would be a better alternative.
Now the games, PC original games would cost just 200 - 500, with the not so original ones costing...well nothing. PS3 games on the other hand would set you back 2K per new game purchased.
Another alternative for PS3 games would be to get used one which would be cheaper but still approx 900- 1400 depending on the disc.
Considering you love to play games, I assume you love to play at any graphical setting in which case I suggest you go with PC. But you would be loosing out on a lot of mind blowing PS3 exclusives - Uncharted - 1,2,3, MGS4, God of war 3, Red dead redemption, the last of us, Killzone - 2,3 .... and the list goes on