Your question confused me a little...
What you are looking for is a small, lightweight screen that can be hooked up to a console, and you want to know if a computer monitor would work, right?
If that is the case, on most modern consoles there are various connections. If you want to hook up a console to a monitor, then I recommend looking for a monitor with an 'hdmi' connection, because both the xbox 360 and playstation 3 offer hdmi slots. Just be sure to buy the hdmi cable separately because the monitors usually do not come with them.
Here are some recommendations from me:
The Monitor: It is 20" and $120
The Cable: $4. This doesn't matter as much, just make sure you get an hdmi cable.
The hdmi cable transfers noise too, and the monitor has built in speakers, so he will be able to hear it.
Hope this helps.
And, if it is not what you are looking for... ignore all of this.