@dsperber thanks for info. One last stupid noob question - can the viewer watching TV on an extender press 'record' ?
Absolutely.
And if you had up to five family members in up to five separate rooms watching "live" TV or recordings through up to five separate extenders and HDTV's, and you had sufficient tuners in your HTPC to support them all if they wanted to watch "live TV" (subtracting any tuners currently being used in the background to perform scheduled recordings) then they could each be doing whatever they wanted independently of anybody else.
And just like with your cable/satellite DVR, WMC provides a 30-minute accumulated buffer of whatever has been played so far in the current program on the current channel you're watching. So pushing the REC button will instantly start recording everything for the current program (up to the end-time as shown in the GUIDE), not only from right this instant but going back as far as the current program exists in this 30-minute buffer (but going back no further than the start of the current program).
In other words, WMC treats your push of the REC button as an in-flight command to instantly start to record the current program being watched, defined by its start/end time in the GUIDE, going back as far as possible in the currently active buffer and including that as well on the recording and ending when the GUIDE says it ends. This is exactly how the recording would have been made had you previously scheduled it, except that you're "coming in part way through the program" so it can start right now and will also pick up as much buffer for the current program as has accumulated before you decided to push that REC button.
This is the same as would happen if you were sitting at your HTPC and watching TV in a window on your monitor (or possibly on a second monitor), while you were working on something else in another window. Then you decided to push REC (using your WMC remote, pointed at a standard WMC IR receiver on your desk). Again, an extender is truly a mini-WMC in a box located somewhere else in your house. So whatever you can do on the HTPC itself, you can also do on any extender... including pushing the REC button while watching "live" TV.
And of course you can PAUSE while watching "live" TV (or watching while simultaneously making a recording, either scheduled or via REC), rewind, start over, skip forward again, etc., all of which has ZERO EFFECT on the ongoing recording which proceeds normally and uninterrupted in the background by whatever you happen to be doing in the foreground. You can even then decide to change channels and watch another program "live", with the previously triggered recording (from your push of the REC button while watching a different program) continues unbothered in the background. You can even power the extender off and go to bed, and the recording you triggered via REC will continue (being performed by the HTPC "server", of course) in the background, having nothing to do with the availability of the extender.
And you can stop (i.e. "abort") any recording currently in progress (either previously scheduled or via REC) just as easily, if you change your mind about it. Whatever portion has been made so far will end up in your list of recordings, and you can certainly watch that piece. Or, you can just delete it and never watch any of it. Again, this can be done from anywhere... on the HTPC (i.e. "server") itself or from any of the extenders (i.e. "clients") which are just mini-WMC boxes remotely placed around your house.
The one thing you can only do on the HTPC itself is to use the mouse or keyboard of your HTPC to control WMC, in addition to being able to control WMC using a standard WMC remote and standard WMC IR (USB) receiver. From an extender, which has no mouse or keyboard, you obviously can only use the remote which came with it (or, actually, any other WMC remote will also work). These are actually all using the same "standard WMC" IR codes defined by Microsoft, so you can find many manufacturers had at one time produced WMC remotes which are physically different but universally interchangeable. They obviously have different ergonomic designs, but they are all usable with all extenders or with the IR/USB receiver up at your HTPC. All WMC remotes can be used everywhere, no matter who made the remotes. They ALL have the same minimum set of WMC-related buttons, though some remotes may have additional buttons for multi-device control or extender-specific functions (e.g. powering on the extender and related TV), etc.
Most importantly, you can allocate however much disk storage space you want to your "\Recorded TV" folder, which is used to make new recordings. And then if you want to make more room for new recordings, you can move old recordings to any number of other additional folders on the disk drives of the HTPC (or on a network server!) which are defined as part of the "Recorded TV Library", used for playback and for the list of recordings available for playback.
So really you can have an infinite amount of storage for recordings to be played back, but are limited to one physical drive (ie. one folder) for storage of newly made recordings. But once the recordings have been made you can move them elsewhere, with them still being available for playback while making room for still more recordings.
