For your purposes it's probably best to stick with Memory Map. You don't need to buy the latest version, you can upgrade to V5 for free but you should PM me to find out how to enable it to read your MM2004 maps (it won't read them as supplied, thanks to the cursed OS).
In fact this is one of the best reasons for sticking with MM, and may well eventually override all the technical aspects of the software. All mapping companies are forbidden from allowing major new versions of their software to read maps issued with previous versions, but MM is the only one where this is easily circumvented. For all other products, you would either have to run several versions concurrently to cover all the map versions you have bought, or alternatively fork out and buy new versions of the maps even if you don't want them.
Other related facts about the mapping products:-
MM is the only one whose OS-imposed restrictions can be easily neutralized.
MM and Tracklogs software installations are not (technically speaking) limited to one particular PC or hardware configuration, you can install them on any PC anytime.
Anquet and Quo installations are limited to one PC by a registration scheme and have to be activated by a code specific to that PC (in the case of Anquet this can in fact be circumvented). This activation process also means that any change to the hardware of your PC might mean grovelling to Anquet or Quo for a new activation code.
