An interesting article (especially for Keith) on stealing cars shows how computer security as a topic is becoming increasingly pervasive. There is anecdotal evidence that some new cars (BMW X5s are mentioned in the article) that use keyless unlock and start mechanisms can be spoofed by a sufficiently intelligent attacker.
The article mentions laptops being used for this, implying that any off-the-shelf laptop would be capable of this, although this seems unlikely -- the radios in standard laptops are set up to run in the 2.4Ghz range (both Bluetooth and 802.11 operate in this frequency band), and I believe the BMW keys operate at around 300Mhz.
Bad security or urban myth? Hard to say at this point.