Powering a reprap with an unregulated power source?

I'm building a prusa i3, and now I'm in the process of buying/building a power supply... I have a atx psu that I've hacked, but I have my doubts about using it... It's only 17A on the single 12v line, and I bought it used...

I have a lot of transformers laying around, and rectifiers capable of delivering higher currents, but I've only built regulating circuits of a few amps....

Does anyone have schematics for a high current regulation circuit, or is it possible to run a reprap off a unregulated 12v power supply?

(pardon my English, and the potential consideration of this as un utterly stupid question, I'm Swedish)

here is a good thread on the subject
[forums.reprap.org]

The heaters don't need regulation, but the logic-side does.

I was using a salvaged ATX and had 5V 50mV peak--to-peak 50kHz noise feeding into my system and confusing my ADC. Filtering the +5 for my cheap electronics cleaned that problem up.

Thanks for the replies!

I'm going to read the other thread, and see what options I have...

I don't think the atx PSU I have is that bad though , I connected a small DC motor to it and managed to get more then 12A from it without it shutting down... Strangely enough, when I connect my amp meter in series with the motor it works fine.. I can put so much load on the motor it stops, without the PSU shutting down... Without the amp meter the PSU shuts down as soon as the green wire to a black one ... If I tap the green wire rapidly I can get the motor spinning, and then it works as normal.. If I put a load on the motor the PSU shuts down before I manage to slow it down to a stop... How can that be?

The inrush current of the motor looks like a short circuit and the power supply shuts down. The amp meter is a resistance that limits the inrush current so the power supply doesn't go into shutdown. Tapping the wire rapidly also limits the current and allows it to start.

Thanks for the reply! So the resistance of the DC motor is to low, but that shouldn't be a problem when the PSU is connected to my arduino/extruder/hot bed etc, right?