and welcome to BleepingComputer
I think that the only way you can view this archive is if you are logged on. I'm pretty sure that the archive is stored as a .dat file. This means that you can't read the contents unless you decode
it, as it would be in hex code (basically a load of numbers). If you go to your All the archive files are stored inside the Yahoo!\Messenger\Profiles\user id folder
and look for the relevant .dat file for your user and try and open it with notepad (right click > open with) you'll see that it's just a collection of numbers that don't make sense. If you want to be super sure that no-one can decode this, even though it would be very compicated, you could cut that file and copy it to a CD
and replace it when you get back from your break - you'll have absolute peace of mind that no one will be able to access your archive.
I hope that helps, and let me know how you get on.