web design

Pretty much now a days if they dont' have the correct plug in it will prompt them to download it - with you doing nothign - but what you could do is have a link on your site saying something like "if you have problems viewing the content click here to download the latest flash player"

also having the browser check there plugins is very tedious since IE, aol ie, netscape and all the verison in between.

then have a link that takes them to the flash download page at:
http://www.macromedia.com/software/flash/download/

if you want to copy flash to your own server to have people download from contact them to see how to mirror there site.