If you have a limited number of columns and a unique key in both lists to match
up...
You may want to try this.
I'm assuming the key data is in column A of each sheet--but it doesn't have to
be.
Start a new worksheet
copy the key data from sheet1 to A1 of the new sheet
copy the key data from Sheet2 under that list in column A of the new sheet.
(include a single header row in row 1)
Now you have a giant list in column A--but it may have duplicates.
Select column A of that new worksheet.
Data|Filter|advanced filter
copy to another location (Use B1 of that new sheet)
Check unique records only
Now column B contains a unique list based on both sheets.
Delete column A (we're done with it).
Now you can use =vlookup()'s to bring back the data that you want from each
sheet.
You could use column's B and C for the same field from sheet1 and sheet2 and
then use a formula in column D indicating a difference between B and C:
=if(b1=c1,"","<---")
If your key column isn't in column A, then you could do the same kind of thing
to build the unique list. But then use =index(match()) (instead of =vlookup())
to return the data.
You may want to read Debra Dalgleish's notes:
http://www.contextures.com/xlFunctions02.html (for =vlookup())
and
http://www.contextures.com/xlFunctions03.html (for =index(match()))