Installing Mac osx

I am a PC guy and I am installing a newly "Obtained" copy of OSX 10.4 because she still has 10.3 my question to you bucnh of helpful folks is if I install it as an upgrade will it erase her current files on the disk. Does the install format the disk automatically or will her 5hit be safe? ANY info you guys and gals could pass along would be helpful here. I need to learn mac stuff too. Thanks again:)

No you wont lose your files...
I installed Mac OS 10.4 on a Mac OS9 machine, and it kept all my files.

Im gonna try it today wish me luck

i need a little help on installing mac on pc it wont just install on my intel pc