Wow, you and your complex projects...!
1. "given the remote computer is setup to allow such a connection" - meaning what? The only obvious way I know of is with a FTP server... something like:
1. User registers and provides his/her IP, FTP port, username and pasword.
2. PHP can then parse all directories there and store them on the server...however you'd want - when the user logs in, when the user presses a button, etc.
or display a real-time listing of the directories (both require parsing the info for a nice output).
3. The user can:
a. Log in and view the files...and this is where it's a bit odd. You can use the server as a go-between (higher chance for latency issues/more bandwidth unnecessarily used?)
b. Provide a direct FTP link.
Obviously I've never done any "streaming", so I'm not sure what all is involved.
...hmm...perhaps you can use AJAX! Break the file into small pieces, and based on the bandwidth, get the latest pieces of data from the server...haha!
And I am sure there are better options - but what they are - I have no idea!
Hah, I know that didn't help much... anyways, I think your two player PHP game would be much easier - as long as you are familiar with MySQL too, and you're not afraid of either using javascript's XML object
or constantly refreshing the page...as all it would be doing is updating the page based on the mysql database info.