Excel 2007 : compare two sheets and find differences

I don't know why I'm having such a hard time doing this. I've found multiple answers on this site listing how to compare two sheets and find the differences but none seem to be working for me (sometimes I get N/A errors, sometimes it's a circular reference error, and sometimes it says a name is not on the other sheet but when I double check it, it actually is on the sheet. These are the formulas I've been playing with that I've found in different threads here.

=IF(ISNUMBER(MATCH(A1,Sheet1!A:A,0)),"on sheet 1","not on sheet 1")
=if(isnumber(match(a1,sheet2!a:a,0)),"on sheet 2","not on sheet 2")
=IF(VLOOKUP(A1,'Sheet B'!A:B,2,FALSE),"","Available in B")

Here's what I have in my file...

My sheets are called "mine" and "theirs". I have one column, Column A, on both sheets that contain names. There will be duplicates on both sheets and, also, both sheets will contain names that the other sheet doesn't so I'm assuming I'll need to enter a formula in B1 on both sheets.

If someone can help me just start from scratch and tell me what I need to put and where, I'd really appreciate it.

Thanks!