I've use the s-video output from a basic Sky Digibox for years and have great quality. The SKY+ boxes with s-video output should be the same (I guess you can only record from the single tuner that is showing on the TV).

You have 3 options for connecting to a PC
1. Composite - via a SCART to composite adapter (3 phono)
2. S-video - via s-video output of Sky+ box.
3. S-video - via a RGB SCART to s-video powered converter (£30+) and SCART adapter.

(2) is the best quality and easiest choice.

You have 2 options to received into PC.
1. VIVO or a cheap TV card. Not great quality as all encoding is done via software
2. Hardware encoder PVR card (e.g Hauppauge PVR-150 @£40ish). Great quality, accepts s-video input and uses virtually no CPU.

(2) is best choice though costs.

This is for live TV, I assume it is clear that recorded programs cannot be copied directly from the drive but can be played via the COPY option and recorded on the PC using the above (I've not tested that the s-video works for this as only used to copy to VCR via SCART).

Most good PVR software supports the above setup and also provide functions to automatically change channel etc. (with right hardware) to allow full unattended recording. I use GB-PVR - great software, but then do you want to turn your PC into a HTPC PVR or just copy Sky recordings across?

Hope this is of some use and I've not missed your point entirely!