a couple of questions...
First... I assume your HTPC is already hooked in to your TV / Sound system, correct?
Second, from the sounds of it you plan on using it mostly for gaming correct?
Third how far from the TV is the HTPC? And how far from your couch is your TV?
If used for games I would rule out the remote desktop or even VNC thing for that matter immediately, it will not work
If using it for gaming what types of games will be played more so? Action or sports types where the gamepad is used more, or FPS where the keyboard and mouse are used more?
Is it easy to hide cables going from the HTPC to the TV?
I know that may seem like a lot of questions but it helps narrow things down a bit.
I have two Bluetooth keyboard and mouse sets. The First is a logitech MX5000 set. It has a nice layout and a nice laser mouse, and since it operates on bluetooth the range is good. But I notice too much lag in this set, and doesnt seem to be the most reliable at times as sometimes it cuts out easier at longer distances.
The other bluetooth set I have is the MS one that is blue in color. This set feels much more responsive but I don't like the scroll wheel on the mouse as it doesnt have that tactile feel to it, kinda loose and mushy feeling. The keyboard is nice but much larger than the logitech.
I also have a older gyration mini keyboard and mouse. The mouse doesnt do it for me at all in FPS games, and not enough buttons. The shape is odd and doesnt make playing for long periods comfortable. The keyboard is nice and has a nice cover so stuff doesnt get spilled on it and ruin it. The range is nice as wellgoing much further than most other RF sets I have had.
Sadly I like my MS infrared MCE keyboard better for FPS when it comes to reliability and responsiveness. But then I need a decent mouse with good range, I have a RF lasermouse from logitech but past 5 feet it doesnt feel as nice and responsive.
If going corded I would highly reccomend the Active usb extension cables. if needed you can run it to a hub from your HTPC and put the hub in your equipment rack by your TV, then have another active extension cable going form the TV to your sitting area for your keyboard, and yes sadly another for a wired mouse. Another suggestion. If playing mostly FPS games a USB numeric keypad works wonders, you get plenty of buttons and a smaller formfactor.
Now if you primarily plan on using a gamepad I have had great luck with the logitech series of wireless gamepads. The range always seems to be good on them and batterylife is pretty nice as well.
recently though I went another route as I got tired of paying a lot for gamepads and having different gamepads at each PC. I went out and bought a few cheap madcatz (or even gamestop branded as they are the same) XBOX wireless gamepads. The range is good on these as well as battery life. They are incredibly easy to mod in to a USB controller and you only need XBCD downloaded to use it on XP or vista. Since they can be found for $19.99 or less they really are the best bang for the buck. I don't notice any lag to them or the logitech controllers (unless the batteries are dying of course lol)
With wireless game pads I feel confident you could run a active extention form your HTPc to your TV and put the gamepad receiever there.