SLOOPERCAT, I switched two old laptops from Ubuntu back to Windows because of update problems like yours. I am running
OpenCPN 4.8.8 with Windows Vista on one and Windows 7 on the other. I tried
OpenCPN 5 with both but had problems with OpenGL--old versions of Windows don't
work well with it. OpenCPN 4.8.8 doesn't rely as heavily on OpenGL as version 5. You may be able to resolve that issue by downloading better OpenGL drivers for XP, but finding
software that works with such an old operating system may be difficult.
Don't even think about Windows 7. My W7 computer is a real dog--although it worked very well with Ubuntu 12 and 14. You'll get better performance with Windows XP (you probably don't have a choice anyway, as your computer probably won't support anything newer than XP, based on what you've said about its age).
Keep in mind that if you use an older version of OpenCPN plugins (other than those bundled with the program) won't
work. I've never needed the plugins, so that hasn't been an issue for me.
Version 4.8.8 supports
AIS. I have a dAISy receiver which plugs into a USB port and cost about $50. Set up was pretty simple. On rivers it might be nice to see what's around the next bend in the way of big vessels. In my home waters it's a useless, but fun, toy.
Fabbian