I'm just trying to get a grasp on your terminology., I've never used flip4mac to watch something before it's been downloaded. So by download do you mean you already have it on your computer, or is it out on the internet?
1. If it's out on the net, and a large file, and you don't have a fast internet connection, then it could easily take 5 hours to download to your computer.
2. if It's on your computer, and you are loading it into flip4mac, then it may just be an incompatibility issue. If you search, you can find wmp9 for os x out there.
3. If you are downloading the file with bit-torrent, then that can also take a very long time due to a number of factors regardless of your internet connection speed.
4. If the file is on your computer, not the internet...then click the file you want to play to highlight it, and then use the apple+i key to see all of the info about the file.
I hope some of this helps, and if you have more questions...by all means post them.