Step-by-step:

1) Open the worksheet in Excel.

2) Select all the cells that contain the data you want to import, including the column headings.

3) Choose Insert | Name | Define.

4) In the Define Name dialog, type in the name you want to use for the range you have selected, e.g. Export, then click Add, then OK.

5) Save and close the worksheet.

6) In Outlook, choose File | Import and Export.

7) Choose "Import from another program or file," then click Next

8) Choose "Microsoft Excel," then click Next.

9) Select the file and make your choice for duplicate handling, then click Next.

10) Select the destination folder, then click Next.

11) Click Map Custom Fields. Make sure that your Excel fields are all mapped to Outlook fields. Drag field names from the left box and drop them on the names in the right box.  To check the mapping with real data from your file, you can use the Next and Previous buttons at the bottom of the dialog. Click OK when you're done.

12) Click FInish.