Best to use the VLOOKUP function. See this SO post for a similar question and answer: Join two spreadsheets on a common column in Excel or OpenOffice
You can also use MATCH (I'm not sure if MATCH his more efficient than VLOOKUP). Let's say that Sheet1 contains:
Col A
pass1
pass8
pass3
and that Sheet2 contains:
Col A Col B
pass1 info1
pass2 info2
pass3 info3
pass4 info4
pass5 info5
pass6 info6
pass7 info7
pass8 info8
pass9 info9
pass10 info10
Then copy the following to cell B1 in Sheet1 =INDEX(Sheet2!B1:B10,MATCH(A1,Sheet2!A1:A10,0),1)
then fill down to enter the rest of the rows.
Result in Sheet1:
pass1 info1
pass8 info8
pass3 info3
Hope this helps...good luck, Paul