i've just ordered an x2 4400+ to replace the 3500+ which was shipped with the pc, my motherboard is an asus a8n-sli deluxe. i've been told i need to update the bios settings for this but i'm a bit lost as to how i do this, can anyone help?

Probably the easiest way would be to go here:
http://support.asus.com/download/download.aspx?SLanguage=en-us

and dowload the latest bios

then click on "start", "programs", "asus", "asus update".

Select "update bios from a file" and let it do it for you.

That asus update program does have an option for updating from the internet, but I have never had any luck with it. It never finds the newest versions for me, which is why I am recommending the above procedure.

Good luck!