Computer help: windows 98 setup formatting???

windows 98 setup formatting???

Ok, I posted earlier about the display problem, (I only get 16 colors) I just "finally" got the win98 setup to start working and then I get a message that says "Your computer already has an Operating System installed, which cannot be upgraded by this version of setup. You need to obtain the Windows 98 Upgrade." I think my daughters boyfriend installed win98 with his own disk. Is there some way that I can take off his version, and then install my version? Is that formatting, Am I making sense? How do I format? I don't want to go buy an upgrade, when I already have the original disk. I also have the startup floppy that came with the computer, but I'm not sure how to use it. What am going to do? I just want to see photos and videos again. Please help, Jenny
AMD K6
316mb ram
win98 (need to uninstall or reformat?)
I have the win98SE cd disk
and startup floppy that came with pc
I have a dsl modem, and can call someone and talk with them as they help me walk through this mess. email me your phone number and I'll call you. Or if you want I'll give you my number, or just answer my posts, whatever is best. but please help, I'm so lost with this computer stuff, just want to see my photos again.
usmmjenny@frontiernet.net (plain text only please, I can't see photos or some fonts)