Zeewolf: I had some fun, but TBH these are probably too difficult for me to play seriously. Especially since it seems that (at least in the first game) saving costs money... is there some kind of save function in Dosbox? Like there is in other emulators?
Nope, unfortunately. It was not developed with that in mind, and implementing it at a current state would be very difficult (from what I've gathered), but the source code is there, so if you're a nerd-raging programmer you could give it a try.
But true, it's very "hardcore". Being persistent is probably the only way to go, apart from strategy guides and such.