Microsoft confirmed this update only supports certificates for client-side purposes (e.g., browsing in IE). It does not enable Windows XP to function as a server using SHA-2 certificates (e.g., for IIS hosting).
The PTB designation makes this hotfix highly specific. It was intended for: windows xp kb 968730 x86 ptb hotfix
digital signature and certificate support for older Microsoft operating systems or 512 encryption.
: It allows Windows XP and Server 2003 clients to obtain and process certificates from CAs configured with SHA-2 256, 384, or 512 encryption. windows xp kb 968730 x86 ptb hotfix