Most solid solution is to buy a GPIB PCI card, but it is common with software driver incompatibility problems for most of these the less known brands of cards. Cards from Agilent and National Instruments are however very reliable, when they once have been setup. Unfortunately are they expensive even when sold as used.
Both Agilent and NI do also have GPIB-USB converters. Still expensive, at least for a hobbyist.
Cheap PIC converters are seldom halfway GPIB protocol compatible, have not seen anyone yet. Another problem with these are that they not are presented as a GPIB interface in the computer. They are usually delivered without GPIB drivers and installed as a rather slow COM port.
Software designed for high speed GPIB communication VNA-PC do then not work with these converters, because that they only handles GPIB interfaces and/or full speed triggering of VNA is not possible.
If it is enough to just read a screen dump or get some Sxx measurement values and you can accept to wait a second, then can these cheapest converters be an alternative.
However if you need real-time data at PC screen, directly from VNA, such as the antenna tuning software from
http://www.antune.net, then you need something better. A by me verified and recommended fully Agilent compatible GPIB-USB converter with reasonable cost:
**broken link removed**
Can also be found at Ebay. There are also other noname GPIB/USB converters sold at Ebay but this is the only one so far that I can recommended for serious use.
Cost is about $100 for a fully GPIB compatible PC port. Hardware is delivered with all needed drivers. I have my VNA constant hooked up to a computer. Actually do I have the VNA below the lab bench. Saves a lot of space (and noise), even if I instead now have a 24" PC screen at bench.
Can save data whenever I want, directly in PC and if needed, directly have other software to process that data further.