haha, paranoia is good
Don't forget to update the Core and MD with the same settings(speed, dup) though
sh int afterwards is fine. for both of the interfaces. Lots of Runts and drops are not good.
Take a quick look in the syslog as well just to make sure(that all is ok with the 3550).
Not sure how to do a similar in linux though =/ but that will give some hints if this is related to the network which I actually doubt.
(hari posted some nice commands to be run as well)
Btw, I assume you have everything on the inside of the Core, as recommended ?
Is it easy for you to move(copy) the same Movie to the hdd of the Core and view it from there as well?
Just to easily eliminate eventual troublecausers.
Also I posted a while ago about twitchy playback and got the recommendation to not use alpha blending.. Try changing that.(in case you are)