What you are looking for is Adobe Flash 10.1.  The currently the Flash player, 10.0, will not work with mobile phones.  It is going to be avaliable for Android devices that support Android 2.1.  The Eris should be getting it's OS update some time in the first half of this year.  Adobe is also scheduled to release Flash 10.1 in the same time frame.  So hopfully this will be supported on the Eris some time between now and summer...

Of course Verizon may decide that streamign videos will take up too much band width and not let it on their phones period.....  Time will tell...