Hi. I feel really silly asking something like this, but I have tried and I cannot find it anywhere! Okay, here goes: what is the maximum current that I can input to the an ATmega328 to power it, or is the current not really important? Thanks.
It's really an incorrect question. The load (The Arduino) determines how much current will be drawn at a specific voltage, not the voltage source.
Just provide the proper voltage level and as long as the source voltage can provide the current required it does not matter how much more current the voltage source could provide. Your voltage source could be rated to be able to supply 100 amps, but the Arduino would still draw the same current as from a supply rated at 1 amp. It's a Ohm's law thing and the Arduino represents the resistance.
Lefty
I see... I knew I was justified in feeling silly asking it. Thanks.
Not silly, there are no silly questions here, except some of my software questions 
Lefty
@qwery
Voltage is the potential or pressure that causes current to flow. You want to provide the Arduino with voltage in the 6-9 volt range. The onboard regulator reduces that to 5.0VDC with a regulator that acts like a variable resistor. Anything over 5 volts gets turned into waste heat.
Once you've got the Voltage correct, the current will take care of itself.
The power supply should have the capacity to support probably at least 500mA or 1/2 Amp. The Arduino itself pulls less current than that, if I remember right, the Poly Fuse pops off at 200mA.