In terms of monitor performance, don't rely on specs alone. Specs published on sites and listed on manufacturer sites/boxes usually don't mean a lot because of variables in testing conditions, and they always want to make their specs look bigger or better than the competition.
The true measure of monitor quality comes in the form of user reviews. Read through people's firsthand accounts on how the monitor looks and how reliable it is. Take a look at newegg.com here:
They probably sell some of the same monitor models in Germany, so just find one that has good reviews (5 eggs) and see if you can get it in Germany.
You'll likely be looking at a 22-24" monitor with a 1920x1200 resolution. That is pretty standard these days, and not really very expensive at all (at least in the USA).
The Radeon card you have says it supports up to 1920x1200 resolution, so that should be fine. As others have already stated, just make sure you have the appropriate output to connect the monitor.
If you don't have the right output on your old card, then a cheap video card replacement will be fine. Something like this (Radeon 3450, fanless, low-power consumption, DVI, HDMI, D-Sub out, runs 1080p video like a champ, $30 USD):