associating rows according to a field

[great.bean]

I am just begining this project, and it is still in the beginning comceptual stages.
I am creating a weekly report in excel '07 that draws information from an online database.

In the report, I'm going to be calculating several things from the raw data so I'll have a data tab, and then the front report tab. This is no problem. The issue is that in the report I need to show in red those fields that have changed since last week. Now to do this I can set up a macro that will copy the data in the Current Data tab in to a Past Data tab, then import the new data to the Current Data tab. The trouble comes in comparing the two fields. I could set up conditional formatting, but there may be new rows or the rows may not be in the same order. Each of the projects (rows) has a unique ID number. Is there a way to associate the current data with the past data with the ID and check for changes between them? I know this is a database function, but I need Excel formatting for the report and I want to avoid using Access as a middle man.
Any thoughts on this?
Thank you.

[JBeaucaire]

It's totally doable. I would use INDEX/MATCH to create the crossreference, but Conditional Formatting doesn't work against other sheets unless you use Named Ranges. So that will create an additional step.

So, let's assume on PastData the Ids are in column A and you name a sufficient size portion of A as IDs (A1:A1000)

Named Ranges:
A1:A1000 = IDs
B1:B1000 = VALUES


On Sheet1 in the column A1, use this conditional formatting:
Condition1: Formula Is: =INDEX(Values,MATCH(A1,IDs,0))<>B1
Format...Pattern...Red

The ones that DON'T match each week will light up.