It should actually be possible to export and save contacts from Nokia .nfb backups and save them as separate vCard files (.vcf, .vcard etc.) which can then be used to transfer contacts to other software or devices. Such nfb to vcf conversion can be done with various utilities for Nokia phones, such as Noki or NbuExplorer.
Open NFB file Open VCF fileA small usefull program for exploring and extracting of files created with Nokia PC suite
A free explorer for Nokia NBU files