Firstly many thanks to the contributors to http://www.geekzone.co.nz/forums.asp?forumid=34&topicid=13287 which is now closed.

The info in that thread certainly helped but didn't quite provide enough info for my specific situation so this post is to help others that may have the same scenario as me......

My setup: Dedicated Home Theatre PC with a Hauppauge WinTV-3000 (hybrid DVBS/T). Sky dish with a 10750 LNB (Model: Sharp 5A149399, BS1D1AQ112A - you know it's 10750 not 11300 as it's written on the LNB on the dish.  Sky have installed both types of LNB over the years)

My desired result: only to run DVB-S (at this stage) through the media centre interface of Vista. Sorry to those who want to know how to run it dual with DVB-T, haven't go there yet and don't know if I care, only missing Prime.

The long road: after much heartache with positioning the dish as it was out of alignment (I borrowed a freeeview set top box for this as I knew it worked) I had to figure out the settings for the 10750 which were quite different to the 11300.  I eventually got the dish working on the freeview box then after no joy with reghacks and MCE I installed WinTV and eventually through trial and error got the correct settings and presto - all working.  So at least I knew the PC and the WinTV 3000 were functioning ok.

The solution: You need to add this file to the reg:

REGEDIT4

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\HCW88bda\Parameters]
"DVBS_as_DVBT"=dword:00000001 ; Enable remapping support

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\HCW88bda\DVBS_as_DVBT]

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\HCW88bda\DVBS_as_DVBT\177500] ; #5
"dvbs_freq"=dword:BE1040 ; 12456000
"dvbs_polarity"=dword:1 ; 1
"dvbs_srate"=dword:57E4 ; 22500
"nit_onid"=dword:2F ; 47
"nit_tsid"=dword:15 ; 21
"nit_nid"=dword:1 ; 1
"DiSEqC_Port"=dword:0 ; 0
"dvbs_LowOsc"=dword:A40830 ; 10750000
"dvbs_HighOsc"=dword:A40830 ; 10750000
"dvbs_SwitchFreq"=dword:00000016 ; 22

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\HCW88bda\DVBS_as_DVBT\184500] ; #6
"dvbs_freq"=dword:BE79B8 ; 12483000
"dvbs_polarity"=dword:1 ; 1
"dvbs_srate"=dword:57E4 ; 22500
"nit_onid"=dword:2F ; 47
"nit_tsid"=dword:16 ; 22
"nit_nid"=dword:1 ; 1
"DiSEqC_Port"=dword:0 ; 0
"dvbs_LowOsc"=dword:A40830 ; 10750000
"dvbs_HighOsc"=dword:A40830 ; 10750000
"dvbs_SwitchFreq"=dword:00000016 ; 22

--cut here --

Now some notes on some of these settings as you may have a slightly different setup to me.
Note: For those who don't know anything in the file above after a ; is a comment, any changes you want applied to the reg need to be before the ;
dvbs_freq : Frequency in KHz - the Optus D1 sat has the NZ freeview channels split across two frequencies 12483 and 12456, trailing zeros required as they are in Khz.  For more info on the sat go to http://www.lyngsat.com/optusd1.html
dvbs_polarity : Polarity of the signal (Horizontal=1, Vertical=2) Note all reg files I saw had this at 2, I needed 1.
dvbs_srate : Symbol Rate in MSps, Eg. 22500
nit_onid : OriginalNetworkID, network Id on the satellite
nit_tsid : TransportStreamId
nit_nid : NetworkID of the DVB-S stream, terrestrial emulated network Id

"dvbs_SwitchFreq"=dword:00000016 ; 22 - all other reg files I saw had this set to 0, 22 worked as that was the setting that got the freeview set top box going and WinTV for me.

Once you've added the file to the reg - reboot.

When MCE launches you need to re-run the full media center setup (Tasks/Settings/General/Media Center Setup/Run Setup Again), Choosing Australia as the tuning region. (thanks Tom @ playtech.co.nz) Then select Antenna, DVB-T (as MCE doesn't recognise DVB-S card you have to emulate DVB-T) and No to set top box. Then scan for services and you should be home and hosed!