Personally, my belief on looking at data on old computers, is that you shouldn't, regardless of whether the previous owner requested you to delete it or not. Look at file names and file creation/modification dates to get an idea as to when the machine was last used, and what it was used for, and look for any software that you may find useful (as well as any software that you may need to use any gear you got with the machine), but do not look at other people's data.

The reason I feel so strongly about this is because I have had people refuse to give or sell me their old machines (choosing to dump them instead) because they're worried about the safety of their data, and by people looking at other people's data on old machines, its only going to make it harder for us vintage computer enthusiasts to get old machines (and therefore, also parts for old machines) if people get paranoid about their data ending up in the wrong hands. Its hard enough as it is already.

Lets put it this way...how would you feel about someone reading your sensitive personal, business or education-related data?