First you should be aware that Excel is limited to 65,536 rows per sheet (although this is increased in Excel 2007).
What you have described seems an ideal candidate for a VLOOKUP. VLOOKUP is a way of using Excel as a database. The syntax is
=VLOOKUP(what, where, col, True or False)
what is the value that you want to lookup
where specifies the range that you want to look in
col is the column number in your range that you want to lookup.
True looks for the nearest match in a sorted list; False looks for an exact match.
Say you have a list of names in A1:A10, ages in B1:B10 and phone numbers in C1:C10
=VLOOKUP("Colin", A1:C10, 2, False) will give Colin's age
=VLOOKUP("Ben", A1:C10, 3, False) will give Ben's phone number.
what must be to the left of the data that you are trying to look up (in the examples, column A is to the left of columns B and C).