alt131 - 7:00 pm on Dec 27, 2011 (gmt 0)
Hi MisterMaster and welcome to WebmasterWorld :),
Yes, posting links is against the rules for the reasons explained in the posts pinned to the top of the forum, and the sticky mail I have just sent. Thank you for respecting the forum policy and helping to make WebmasterWorld a stronger community.
Ok, back to code. I think the first issue is to understand the behaviour of the div with the background images.
As penders has identified, on the provided code it should not be centred. If it is centred as you say, there is something else affecting it, and that may also be causing the unequal margins once the images are added.
So first examine what is affecting the div. For example, have you set text-align:center and/or a padding on the parent?
Second, which browsers and versions are pushing the div across? This is important because legacy versions behave differently to modern versions, and the cause and solution may need to be different. Finally, can you confirm you are using a full doctype.