A standard lojack is a device that tracks stolen objects. It's hidden within the object, and--as I understand it--when it's activated, with it's own independent and isolated power supply, it allows police to track it via radio (which is difficult to block), provided they have a tracking device (currently operating in 27 US states plus DC, as well as 30+ countries).
Typically, it's used for higher end vehicles. It doesn't prevent theft, ofcourse, but it gives you a much better shot at recovery.
The lojack for laptops, however, is a software feature that uses the internet to keep track of the laptop. Probably not as handy as the vehicular version, but at 25-35$ for a year's protection, atleast worth looking into.
http://www.absolute.com/products/lojackforlaptops
Germany has the internet, right?
As far as chaining it to a radiator, that kind of goes a long way towards defeating the purpose of having a portable laptop in the first place, doesn't it? A lot of effort, trouble, and ugliness for a method that can be defeated in 2 seconds with bolt-cutters (or a hatchet, or a hacksaw), even if not every casual thief will have them.
And if that's going to be your solution, I'd rather invest in a heavy duty metal box with an integrated lock--as in, one that can't be cut with boltcutters. You can still secure that to whatever, and also hide it somewhere. The advantages are that it doesn't immediately visually announce "expensive laptop" to the world, it greatly reduces the impact of any brute force, as well as accidental drops/impacts (hint: pad the inside), and it's both easier to retrieve your laptop from, and a lot harder to cut open than a bunch of chains or a padlock or whatever.
If you can get one that has a decent quality integrated lock *and* that can be padlocked (double padlocked, preferrably, much harder to knock open with an axe that way, and forever to saw through), so much the better.