Following my previous post about the trouble I have had getting the Bluetooth hardware in my Dell Latitude D600 repaired, I then had to reinstall the Dell TrueMobile 300 Bluetooth driver. During the three week wait to get the hardware repaired, I had installed Windows XP SP2 and as Stuart Preston reported on his blog, the Dell drivers do not function correctly under SP2, resulting in a requirement to use the native Microsoft drivers (which are less functional).
A hunt around the Dell Community Forum revealed many unhappy users (bizarrely mostly blaming Microsoft for releasing SP2!), but no real solution until a Google search came up with Dell support document FA1090448 (a search of the Dell website had failed to locate this), pointing to an updated driver that seems to fix the problem.