The ClarisWorks functions LOOKUP, HLOOKUP, VLOOKUP and MATCH are similar to a lookup in FileMaker but for a Spreadsheet. There is one major difference though. The values in your lookup range need to be in ascending or descending order. If the range is not in order then you will get unexpected results or an error of "#N/A!".
Appendix A of the ClarisWorks User's Guide has more information regarding these Spreadsheet functions.