Volts are easy...120v unless you have something that runs at 240v

I've yet to see a US TV or PC that requires 240v (some are switchable)
Watts & Amps is what you need to be concerned with
Usually you allow 5a for a computer (600w)
My 42" LCD TV uses just over 105watts
Stereo may use 200w
So you might have 950w Max depending upon your devices
You would need to know what else is on the exisitng circuit
You should verify this before an electrician comes in
Determine what lights & other outlets are on the same circuit
What size breaker serves the circuit - 15a (1800w) or 20a (2400w)
Determine if you have an open slot in your breaker panel in case you need to add a circuit
Then at least you will be able to tell the electrician what you have & may possibly want
Getting an electrican around here to install just an outlet can be difficult
Some may charge a Min $100 charge...more if they need to run a circuit
Depending upon the room it may need to be AFCI protected - that's ~$35 right there