Turns out I was using the "Video Decoder" tab instead of the "Custom Filter manager" tab to install the ffdshow raw video filter.
It works now, but not very well, unfortunately.
I get this onscreen display (see below) which you must recognize during very choppy You Tube playback, and SVP even adversely affects playback of local files unless I turn SVP off.
I am unable to lower the video profile below 720x576@25.
Is my system too underpowered for SVP? My system tray cpu monitor reading doesn't match (is lower than) the onscreen reading I get from SVP
I've added further system info below
edit: Follow up shows that if I exit SVP Manager and use only SVPTube, You Tube playback works pretty well, nice and smooth.
Potplayer did crash during a You Tube playback, but it was directly after I shut down the SVP Manager, so maybe the cpu was still affected, but subsequent trials have so far gone smoothly.
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SVP_3.1.4.exe
PotPlayer 1.5.36147
XP PRO SP3
IE 8
FIREFOX 19 & 20B4
nVIDIA GeForce GT 610 (GF119)
GeForce 310.70 - WHQL Driver - Dec 17, 2012
DualCore Intel Pentium D 805, 2666 MHz (20 x 133)
2 gb ram