Anyone here like to help a novice with PowerPoint ??

I am putting together a PowerPoint Presentation for a group of Master Gardeners and I have a million questions. I have never used PowerPoint on anything except my own computer,and I don't want any surprises.

First question: Will I have any problems with a version issue?? I am creating in 2003, and have tried to open it on several different versions, the oldest being 97 which will read it on a floppy, but won't read my CD. But that is an older computer and it has alot of quirks anyway, so I don't think I have a problem there.

Secondly: I am asking for a computer projection screen on the wall, this group could get pretty large. Will I see the same picture quality on the huge screen that I see on my computer now, or will it get worse with the large screen? I'm wondering if I need to see if the local school has equipment I could "try it out" ? Is that necessary?

Third for right now: I read some online tutorials that said not to make the presentation too long, what is too long? Am I dealing only with keeping the interest of my group, or the storage factor on my CD? Since I am showing alot of pictures of flowers and plants, I'm getting long.

Hopefully there is someone out there who uses PowerPoint regularly, it's just play for me!!

Thanks alot! Legit