I finally stumped up the cash to buy a second hand Focusrite Scarlett 2i2 usb/audio interface. Yes, the fact that it’s beautiful to look at influenced my decision, but in order to loop on the laptop, it was essential to minimise latency.
I plugged it into my XP laptop, installed the driver, all worked fine. Until, at irregular intervals, the audio out was replaced by a series of “digital clicks”. Going to the hardware setup, tweaking (and restoring) the buffer size brought things back. Later on, I’ve discovered you can reset the processor by double clicking on the CPU meter, top right.
After several weeks of utter frustration, I happened upon a google link which mentioned wi-fi causing issues. So I disabled it and Lo! the problem vanished. How utterly weird, but also wonderful, since it seems to crash no more than once a night, ideally during soundcheck 😉
I should say, this probably isn’t an issue on more recent versions of Windoze 😉