You won't get HD through Scart - you should get it through DVI using an HDMI-to-DVI cable provided there's no problem with the HDCP 'handshake' between the Freesat box and the TV. Should be fine - I run Sky HD via HDMI-to-DVI into my plasma without problems.
But bear in mind that DVI doesn't carry audio, only video, so your TV will also need audio inputs and a separate cable from the Freesat box.
Anyone done this and can confirm? Or indeed let me know what your TV is and I'll do some more digging...