There are still many Windows XP users, and the current version of BatteryCare (0.9.6.3) does not support power plan switching in this system, only in Vista/Seven.
But that is about to change because the power plan auto-switching for XP is now ready for launch on the next version. It has been tested thoroughly and it’s ready for every one of those XP users.
Version 0.9.6.4 is excpected to be released in the next couple of days.
PS – I am writing in english from now on because BatteryCare is now spreaded across the globe, fortunately