what i am wondering is.
can i connect my laptop to my tv via hdmi cable and record what ever video is playing on my tv?

Simple answer, yes, and no.

Various MediaCentre versions have the software built in, and you can buy (or download free) TimeShift or recordinging software, but your PC must have the hardware in to do it.

I'm guessing your PC has a HDMI output, and that's exactly what it is, an output, you can't use it for an input signal, the same way that you can't use the input on your TV to broadcast.

You can buy all kinds of TV PCI/PCMCIA cards, Dongles and other USB devices to connect Aerials, CCTV, Camcorders and the like to your PC/Laptop, they can be quite cheap and most will come with the basic software to record with them.

yeah i have a hdmi connection on my pc and tv and i have nch software on my computer to record.

so do you think this would be all i would need?

No - as TheDr said your HDMI output on your graphics card is an output. You need a receiver card. You're using a desktop machine so you need a PCI TV card. Ebuyer.com for cheap ones.

The way I do it is to record to Sky+ and then copy to DVD.

I'm sure other set top boxes with HDD have this functionality?

As The Dr says, you can purchase quite reasonably priced USB type tuner/adaptors which you can use to plug an aerial directly into your pc. You can then record tv onto the computers hard drive and then copy these to a disc or memory stick if necessary.

http://www.pcpro.co.uk/reviews/tv-tuners