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No actual experience of that GTP unit but seems its driven by WinPic800 which only works up to XP.
If it was my choice, I would use your old system to program up a 2550 chip with the Microchips Pickit2 v 232 software and modify your programmer board into the Pickit2 Lite design. ( loads of posts / circuits about it in this forum)
A friend with W7 64 bit says MPlab and Pk2 work fine.
The Pk2 also has the advantage of being able to run the hardware Debugger and the extra USART tools and Logic Analyzer.