Thanks, but no joy here...there wasn't even a 'PanelSizeStore.sol' anywhere on my system.
Somebody on the photoshop.com forums claims they don't have the issue. I did as they suggestes and deleted my prefs etc and still the width doesn't stick.
Photoshop opens, the panel shows up narrow and empty, then part of it goes dark grey and after the icons populate it goes wide.
It seems like a bug in the .swf files to me...maybe an XP thing, I dunno.