Oh, gosh! WMV? The horror!
I would say that for what you're looking for, you should not have too much difficulty. You need only get the charge, anyways, and flag their account for being able to view a particular video, after which they can do what they want with it.
As for formats, avoid that horrid abomination of Microsoft anyway. WMV achieves compression by, among other things, noting differences between frames. As a side effect, if you fast forward or rewind, it can take several seconds before it is able to reconstruct the entire image, during which you see a rather muddy botch of your video.
Stream video in FLV format, which provides excellent compression, and very decent quality, without the bad side effects of WMV. FlowPlayer is a great Open Source Flash video player with lots of options, and it's really easy to integrate.
For downloads, MPEG is probably your surest bet, although OGG Theora is also great. Theora is an Open format, that has codecs easily available for all platforms, and since they're Open as well, you can offer them for download. Theora has great compression, and very good quality as well. Since sound is compressed as OGG Vorbis, instead of MP3 as it is in an MPEG, you're also guaranteed good sound quality. MPEG, of course, is just a well supported standard, and everyone should be able to play an MPEG without a problem, although you'll need to stick to the older MPEG2, and not the newer MPEG4 format for maximal compatibility. Neither MPEG, nor Theora suffer from WMV's diffing problems. MPEG, Theora, and even FLV work just fine in media players like VLC, MPUI (MPlayer), and any Xine derivative.
Oh, BTW ZenCart, which I link to below, is a pretty cool project, and it lists on it's features page "downloadable virtual products", which, I believe, is exactly what you're looking for.
http://www.zen-cart.com/index.php?main_ ... pages_id=5
Hope some of that helps,
OmniUni