The version noted by rick is actually version 2 of GPO, version 3 updated the kontact player to kp 2. This heralded the loss of garritan studio, for reasons best known to themselves, and prompted the need for virtual cables such as midi ox.
version 4 was the start of the aria player and in my experience the most stable and responsive of the products so far, again still can be used as a standalone with virtual cables, if anyone is still interested i would be happy to set it up on my own setup and give a step by step account of what i have done.
They have made extensive updates to the brass sounds making them sound more realistic than ever.
Aria also allows you to put in a midi file to the actual program and assign the instruments to each line and play back within aria itself, making it quite useful for recording purposes.
I am fairly interested in your comment about yamaha no longer working in vista, is this in fact a hardware card or is this actually the software only version. if its the software only version which I have, I have managed to make it work within vista. however I dont currently have it installed as I am far more enamoured with other solutions at present, and it can have an inpact on the vst instruments I am currently using.
you can actually get a copy of windows 98, which i imagine would be fine for the purposes of just running the viewer from computer exchange for about £25.