That's; all over...

January 13th 2010...
No more NAV 4.0 sales, no more fixes, no more work on it - MS Dynamics support is finished for NAV 4.0 (all versions).

https://mbs.microsoft.com/partnersource/support/supportlifecycle/

Dynamics NAV 4.0 SP3 still could be downloaded from
https://mbs.microsoft.com/partnersource/deployment/resources/productreleases/microsoftdynamicsnav40sp3.htm?printpage=false

And latest build (latest fix) could be got as described at http://blogs.technet.com/gediminb/archive/2009/03/26/available-nav-hotfixes-download-using-kb-article.aspx
or directly
http://support.microsoft.com/hotfix/KBHotfix.aspx?kbnum=978896&kbln=en-us