A cluster of computers works well when you can say...
Can I have someone sit at each computer and do part of the problem, and will that speed things up? In other words, can the problem be split into chunks that are basically independent?
Given that you describe the problem as "a large number of video files to transform", yes, this would work on a cluster.
Microsoft does have clustering software that I know nothing about. It might be the way to go.
Probably easier would be:
Dedicate one computer as the master. All the rest are clients.
Put all your video files on this master in a folder.
Make a shared folder per client and have each client mount that shared folder.
The clients run some windows scripting language (perl would work) which wakes up
every so often, and, if something is in the shared folder, renames it to work_yourfilenamehere and runs your transform. When it's done it renames it to done_yourfilenamehere. If not, just wait for 60 secs or so.
The master computer runs a script which looks in each of the shared folders. If they have nothing in them then put one file to be transformed. If they have a file named done_yourfilenamehere then move it to the done folder. Loop until nothing is left in the master folder.
Basically all the clients should be kept as busy as possible, with each client taking what ever time they needed to transform each file.