zzzz243,
This can be tricky, because you do not mention how accurate your data is and how much on the Spreadsheet may be different from the SharePoint List.
Here's a general process that I would start with:
1A. If you have a unique index for these records, you can insure accuracy much better than if not. This should be a standard practice anyway. If you don't have indexes, this could become very sticky.
2A. Create a recordset for the Spreadsheet. Then cycle through the records one by one. As you cycle through, use the index of the record in the Spreadsheet as a search criteria for a second recordset based on the SharePoint list. If it finds a record, update all the values in the Spreadsheet to the SharePoint List. If there is no corresponding record, then add a new record to the SharePoint List.
1B. If you do not have indexes, this can get ugly very quickly. Create two recordsets--one for the Spreadsheet, one for the SharePoint list. Make sure that the queries used to create these recordsets are sorted identically (to the maximum number of levels possible, so all records should correspond).
2B. Cycle through both recordsets record by record and hope that the records match. You will have to evaluate each set of records individually. However, you may have problems with new records in the Spreadsheet. Would all the new records be at the end? Will there ever be a case in which the SharePoint list has new records that are not in the Spreadsheet?
Lots of complexities in the second scenario.
Give us more detail and try some things out and see what you come up with. We'll be glad to troubleshoot and work toward a solution.