The charity staff have a few computers running Windows 7
why on earth does a charity run w7? were those computers a gift?
But it needs to be understandable by the non-geeks in the charity
average computer illiterate users can do absolutely nothing with ms-access. specially smart average computer illiterate users can do utter crap with ms-access in which they themselves will get lost very soon. geeks can use ms-access as they would use any other relational engine (just a very limited one). in short: ms-acces offers zero, it's not really an alternative in this case.
developing something for them (the cited mysql/django approach) is cool but will make them dependent on you. do it only if you reasonably expect you'll be around for a while and are up for the compromise :-)
i second the spreadsheet suggestion. and i would add that probably the best contribution you could make is to train someone in that staff to be self-sufficient in this kind of tasks. it might be substantially more effort but definitely worth it, specially if you make sure he/she passes the knowledge on before quitting. of course, first thing to do is to ask if there's another bizarre requirement for having commercial software. if not, promptly format those bitches and grab free software for them, show them how to start using it.