Vista "Ripcurl" patch on Microsoft Update
The Official SBS Blog : New SBS 2003 Updates released through Microsoft Update and WSUS:
Also on MU today is the “Ripcurl” update
The Official SBS Blog : SBS Vista Client Update (Ripcurl) Now Available:
Ripcurl is the Vista compatibility patch to help get VISTA machines to /connectcomputer easier to the domain.
Now whether you define it as “critical” is up to you