I'm going to be fixing a family friend's computer later and won't be interacting with the computer owner personally, so I would like to have a readme.txt to automatically open the first time (and only the first time) he boots the computer so he can see what I did to fix the problems and what he should avoid having these issues in the future. Is there anyway to do this?
Assuming this is a Windows machine, you could use Task Scheduler that is built into Windows.
Interesting - but why not just an email, so he can review it again if he likes?
Assuming you have your reasons, the method Luke mentions is a good one. On Windows 7 the startup folder for a user is:
Or you can try putting one in the default:
C:\Users\Default\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup (<-- may have to create directory)
Considering your question , you wants to give some useful information and guides for him.
So I prefer instead of showing one time you may request him to save that document for his future reference.
So write the document and store it in some folder and put the shortcut link on Startup folder(Start->All Programs).
In the end of the document ask him to to remove the shortcut link.