Yes, support for SUS v.1.0 will end on 6th December 2006.

After this date it will no longer be supported, but more importantly it will no longer be able to download or distribute any new updates.

So, if you are still running "old" SUS you need to make the more to WSUS in the next month or so. While there is no 'upgrade' as such, you can migrate all your approvals and updates across.

This article covers the basics:
Migrate from a SUS Server to a WSUS Server

or download a Step-by-Step Guide to Migrating from SUS to WSUS

You might also want to consider the Beta 2 of WSUS 3.0, but since that requires Windows Server 2003 sp1 (and a bunch of other components) you could not migrate directly from
SUS if you have it running on Windows 2000.