I'd like to record my son playing the piano.
So basically I'm looking for a cheap but half decent microphone that I can connect to my computer sound card and record.

One microphone I'm considering is the Sony ECM-DS70P, a stereo condenser mic with a 3.5mm jack that requires plug power in order to operate. It seems to be a device targeted at mini-disc recorders.

I have no idea if my Dell Dimension 3100's mic jack is powered or not and I don't have any documentation to guide me. I'm pretty sure it's a fairly standard sound card as I don't remember paying any huge premium for an upgrade.

So, what do you think? Is there any likelihood that it's a powered mic jack? Is there a way I can find out? Or should I really consider a different microphone (if so please suggest)?

I can get the Sony for $35. I look forward to any guidance you might be able to offer.
Thanks!

Voltmeter or tongue (it's only 5V) across the terminals.

Hmm, I'm not sure I can get my tongue into that little jack receptacle. I'll see if I can get the voltmeter probe in there.

From the wiki http://en.wikipedia.org/wiki/TRS_connector
Computer sound
Personal computer sound cards from Creative Labs, Sound Blaster or compatible to these use a 3.5 mm TRS as a mono microphone input, and deliver a 5 V polarising voltage on the ring to power electret microphones from the card manufacturer. Sometimes called phantom power, this is not a suitable power source for microphones designed for true phantom power and is better called bias voltage. Compatibility between different manufacturers is unreliable.
Real phantom power is 48 V.

Recording equipment
Many small video cameras, laptops, Minidisc recorders and other consumer devices use a 3.5 mm microphone connector for attaching a (mono/stereo) microphone to the system. These fall into three categories:
Devices (usually of the "toy" variety), which use a un-powered microphone: usually a cheap dynamic or piezo microphone. The microphone generates its own voltage, and does not require power.
Devices (usually very expensive recorders, for hi-fi or broadcast use) which use a self-powered microphone: usually an expensive dynamic microphone with internal battery-powered amplifier.
Devices (most consumer equipment) which use a "plug-in powered" microphone: an electret microphone containing an internal FET amplifier. These provide a good quality signal, in a very small microphone. However, the internal FET requires a DC power supply, which is provided as a bias voltage.Plug-in power is supplied on the same line as the audio signal, using an RC filter. The DC bias voltage supplies the FET amplifier (at a low current), while the capacitor decouples the DC supply from the AC input to the recorder. Typically, V=1.5 V, R=1 kΩ, C=47 µF.
I don't think it's a good idea to use this Sony mic with your computer. Just take a decent dynamic mic (clone of SM58) for the same price.

WBR, Victor.