Weird looking background

I am still working on my new and only ever flash site…, in my section called “what I have done” I put my portfolio via imported png’s. I used png’s because they come in with no background but are fairly large files that hold quality… on my MAC they look beautiful. on my PC at work, they have like an almost transparent background outlining them… can’t figure out why?
do you see what I see?
do you know howe to fix the situation?

thanks much…