Not much I can add to the above advice.
An SSD might make a huge difference or not much at all, it really rather depends what the bottleneck is. A quick google would suggest that your model is a single core Semperon CPU, in which case you’d probably just be throwing good money after bad. Even when spinning up virtual machines at work running the lightest of OSes doing minimal work, I wouldn’t entertain anything less than two cores.
I think if it were me I’d try a punt on a Linux install and see how that fares, then stick it on ebay / throw it in the bin. It’s an eight year old laptop that by your own admission was crap when it was new, it owes you nowt. (He said, typing on a laptop which had its 11th birthday a couple of months ago…)