Im interested in getting the ability to watch HD on my computer.  I know Freesat is Free-to-air and sky also hass Free-to-view channels so it is possible to get channels without getting Sky.

Has anyone got any experience with doing this?  ie what hardware is required.  Ive never had Sky so we dont have a mini-dish at the moment so obviously I would need to get a dish with the required extras.  Whhich extras Im hoping you can advise

its possible to get sky ;o)

DVB2 Card, Dish, LNB, Cabling (Motor if you want to go down that route - Disecq motor is only about £50 - you will get a LOT more channels if you can have the dish move ;o))
Software to Watch - erm, RitzDVB, MyTheatre, Alt-DVB, ProgDVB are the best 4 & mostly free!!!
CODECS!!!! Good luck there ;o)

That will get you freeview stuff
but.... the good news is the software programs mentioned above support "plugins" & they can Emulate CAM (Card Access Modules)
The best Cam EMU is probably CCAM followed by GBox as these CAMS support Card Sharing... lets say for example you have SKY UK & I have Sky Italia, Someone else has Premiere (German TV),
maybe you know spaniard for their satellite, etc. - well you can share the cards via internet. Legal? of course not, but your technically breaking the law watching foreign TV anyway, so in for a penny.....

http://www.dvbsoft.net good place to start for software
http://www.dvbshop.net/ best place for DVB PC Cards
as for a dish,etc. you can try anywhere..
Any reason you want to go via your PC & Not get  a seperate SetTop Box? Dreambox 800HD has just came out
It runs Linux & has a solid "community" the box supports HD as well as the ability to install a Hard Drive for PVR

oh & theres supposedly a problem getting ITV HD with anything except a Sky Box

What card is good?  What should I be looking for?
The reason I am wanting via pc is capturing stuff.  I do a fair bit and my freeview signal is a bit iffy the further down the channel list you go.
I had a play with the amp after reading that they amplify the interference rather than amplifying the digital signal.  
I went from:
Summary of frequencies
======================

Frequency=754000kHz  Strength=64  Quality=90%
Frequency=786000kHz  Strength=47  Quality=75%
Frequency=810000kHz  Strength=63  Quality=75%
Frequency=834000kHz  Strength=55  Quality=75%
Frequency=842000kHz  Strength=39  Quality=80%
Frequency=850000kHz  Strength=35  Quality=62%
to:
Summary of frequencies
======================

Frequency=754000kHz  Strength=71  Quality=96%
Frequency=786000kHz  Strength=62  Quality=75%
Frequency=810000kHz  Strength=77  Quality=90%
Frequency=834000kHz  Strength=67  Quality=75%
Frequency=842000kHz  Strength=43  Quality=80%
Frequency=850000kHz  Strength=43  Quality=80%

Any idea what the issue is with ITV HD?  It will probably be sh*t anyway

no idea what a good card is as I ditched the PC Sat a while ago & went the dreambox route, so your going to have do your own research there
As for ITV, they broadcast their Video stream as Data & Basically you cant get the picture - this affects the dreambox, no Idea about PC Cards.

^
Yeah its a problem unless you get your software/stb to scan for all services and then sit there looking for the ITV HD stream.
Basically ITV HD is accessed using "the red button" which takes you to an alternate "data" stream. If the software youre running doesnt support the "red button" then its a PITA getting to ITV HD.