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When I search the 'HTTP Client VI' at ni.com, the oldest version that appears in is LabVIEW 2010.
The Telnet VI is part of the Internet Toolkit. According to this LabVIEW 8.5 Compatibility article, LabVIEW 8.5 is compatible with Internet Toolkit 6.0.1. Only version 6.0.2 has the Telnet VI. The oldest version of LabVIEW that can use the Intenet Toolkit 6.0.2 is LabVIEW 2009.
According to the LabVIEW 8.5 manual, there is an HTTP protocol, but I don't know about the HTTP Client VI specifically. Here is the link to the manual page 247: