Computers are ok as long as the power supply is dual voltage 220 - 110 and
most are.
Yes, I've actually never seen a single voltage PSU. I've seen some which
*appear* to be 240V only, but on closer inspection there was just a big
"240V" sticker over the switch. Many things have automatic voltage switching
nowadays, so no switches are required.
but the monitors, printers, and other perifs are all 110 and
should not be used in Europe.
Well that's a half-truth. Most monitors I've seen are multi-voltage (again
most newer ones are automatic), then again many things like printers aren't.
Some portable devices designed for travelling like my USB Zip Drive do come
with with multi-voltage transformers, though, so it's not always the case,
especially with newer products. And with products that aren't supplied with
suitable adaptors, it's very likely that you will be able to get 220-240V
ones from the manufacturers or elsewhere.
You would still have to buy the correct cord for the computer.
All monitors and PSUs use the standard 3-pin AC cords - you can buy these
easily or just change the plug - but make sure it's an EARTHED (3-wire) plug
you're replacing it with*! Also many other multi-voltage things just use
standard 2-pin AC cords (with the 8-shaped plug), which you can also get
easily or just change the plug.
*Make sure the sockets in your house - and your actual house - are earthed
correctly. I don't know what household electricity regulations are like in
Denmark but here in Ireland you're supposed to have the earth circuit in
your house connected to a big rod put in the ground outside. If your house
is made before the 60s/70s you really should get the electrics checked as it
may not be earthed at all! Earthing is very important for things like PCs...