The BBC's released an article last night entitled: "Hard drive evolution could hit Microsoft XP users"
Read it here: http://news.bbc.co.uk/1/hi/technology/8557144.stm
This article seems to have caused a lot of excess worry and confusion for people still using Windows XP. So allow me to briefly put your mind at ease.
What does this actually mean for Windows XP users?
First of all, you do not need to worry about any of this until you have to buy a new hard drive. Nothing will change on your existing computer.
If you are about to buy a new hard drive; There are very few of these "Advanced Format" hard drives out at the moment - and all of them have a "switch" (jumper at the back of the drive) which allows you to run the drive "in compatibility mode" (the original 512-byte format) which will work happily with Windows XP.
In the near future (2-3 years) there is nothing to worry about, hard drive manufacturers should provide this "compatibility mode".
In future (more than 4-5 years time), hard drive manufacturers may begin expecting customers to have an operating system (such as Windows 7) that can support this new format.
As futher reading, I'd highly recommend this HotHardware article for a good introduction to the new Advanced Format:
Exploring WD's Advanced Format HD Technology