Small Business Server 4.0 Upgrade

Easy question:

Can I upgrade SBS 4.0 to Windows NT 4.0 and then to Win 2000 Server?

I tried going directly from SBS 4.0 to Win 2000 Server Upgrade. It does not work. Microsoft is recommending going from SBS 4.0 to SBS 4.5 to SBS Win 2000. This is NOT viable as we have lost the original prod reg key & micorsoft will not send us the free upgrade to SBS 4.5 so that we can turn around and buy the SBS Win 2000 version.

Help. Any ideas?