simple pre-amp for ELF antenna?
The circuit from romero is this: -


Salient points that are noteworthy are the balanced input amplifier which uses a virtual earth thus relying on the DC resistance and inductance of the coil for dictating the maximum gain limit. The OP-07 is a decent choice - it's fairly low noise device and it has a 200Hz low pass filter built in courtesy of the 200pF (C8) across R1 (3.3Mohm). 

Note about it being a balanced amplifier - Electric field pick-up will be common mode to both ends of the coil so you need a balanced input. A balanced input ignores (to a great extent) common mode signals.

You can optionally bypass the Low pass filter stage and drive directly onto the final gain stage so I would consider using the front end of this circuit up to the R17 and the switch and inputting that output via a 4k7 to your sound card. This is the simplest circuit that would be effective.

For a PSU you should be able to run it from any split supply from +/-3V to the +/-9V romero uses. At a push you could run it from a 9V battery with a potential divider (like R30 and R29) but use lower values of resistance (1k won't upset the input balance too much) but put 100uF across each resistor OR just copy romero's PSU.