I think I know the PDA you have - I had one like it when they came out about 10 years ago. Not sure what you paid but I would recommend going with a cheap tablet and not even try messing with "old" unsupported tech.
With that, get some SD cards or a compact flash card as you will quickly need more memory and can load different things on different cards. A good map product is:http://maps.me/en/home I don't know if you can get it to load on your PDA but it works great on phones and tablets as an 'unconnected' map.
You may find this:
https://www.bl.uk/collection-guides/digital-mapping helpful in finding 'generic' maps that could be loaded on your PDA. The device (at one time) I think came with a simple audio player but I'm not sure... it already has a jack for headphones so it was designed for it. Maybe the Dell support site has some info.
I am using a Samsung Galaxy tablet now - you should be able to get them (like the Barnes & Nobel nook) for about $100 US. With an up-to-date device you will have a lot better results.
I've got some older mobile devices I try to keep running and every year they get older the harder it is to keep them useful.
Just my thoughts - good luck!
Paul -