where x is the ip-address of the proxy, and y the port.
Surf to the repository and download the PPD-file. Open it with a text-editor. Identify the line that says <CODEBASE HREF="x86/Convert-ASN1-0.14-PPM.tar.gz" />. Download that tar.gz-file. Put both files in a directory, the tarball must be saved relative to the ppd as stated in the ppd (here ./x86). Add that directory as a repository to ppm.