I have converted a computer power supply to run my A123 Charger, my Twin Peak charger, and my Duratrax Digital fish (can't spell the P word) charger. It was a 500 watt Hercules power supply, very off brand and generic, and I doubt it would power a computer very well, but it only cost me $14 for the power supply with free shipping and it does what I need very well.
For the resistor part, I bought mine at Radio Shack in the form of
this. It has worked great for me so far. I just followed one of those walkthroughs for converting them, and the one you linked to should work great if you get a normal ATX power supply.
Brijar!!!