Conditional Formatting for multiple conditions

Hi, All. I'm not too advanced of an Excel user and would appreciate any help someone can give me with the following:

I'd like conditional formatting to highlight cells that are duplicated if another condition is met. Example:

Shipped Delivered
1 12/21/2012
2
3 12/23/2012
1 12/24/2012
2
3

Only the second '2' in the first column should be highlighted because the first '2' has not delivered yet. I'm trying to avoid duplication of something that is currently in use. Make sense? My first time posting on a forum so please let me know if I should doing anything differently. Thanks!!

Shipped Delivered
1 12/21/2012
2
3 12/23/2012
1 12/24/2012
2
3

'Shipped' and 'Delivered' are two separate columns. I can't figure out how to upload a better image. I don't see the paperclip button. Sorry....

Hi, dilipandey!
Really appreciate your willingness to help out. This is very close to what I'm looking for. The only issue I see with this formula is that it does not continue to flag the duplicates. Once the first '2' has 'delivered', the second '2' is no longer highligthed. Perfect. However, if I enter a third '2' before the second one has 'delivered' it does not flag it. The shipped numbers will be used over and over again, but I want to avoid using one that is currently in use. Please let me know if this makes sense. I'm thinking that my citrix privileges/setting are prevening me from being able to insert a file. Sorry.

Shipped Delivered
1 12/21/2012
2 12/22/2012
3 12/23/2012
1 12/24/2012
2
3
2 (this one is not highlighting)

Thanks!!!!