Vista will not support more than 2 tuners and it's really annoying me, especially now i know it will support 4 tuners but due to something Microsoft have done it's much harder to get them working.

I am thinking of redoing the howto since people still dont get it. 

Also there are a couple of shortcuts that are not in it now.

One easy one is to install all the tuner drivers, then only hook up the cable to 2 of them.  Run MCE or VMC setup.  Verify it is working then export the tuners.  Disconnect the cable and hook up the cable to the next 2 tuners.  Re run MCE or VMC setup.  Verify the 2 new tuners work correctly.  Reimport the registry entry for the first 2 tuners.  Reboot or restart all Media center services.  Verify all 4 tuners are working correctly.

Edit the watch and record orders to suit.

 Yea I might redo it this weekend.  We'll see

Yeah, here's a blog outlining it. Once you figure it out, it's real easy.
Here's how I would do it:

Install tuners
Install drivers
Fire up MCE and configure 1 or 2 tuners. (MCE will only recognize 2 at a time; you'll have to tweak the registry after this next step.)
Download and install this tuner program.

Install it and choose the Get Tuners button (ignore the 'Configure Now!' button completely). The tuners highlighted in red are not configured for MCE. Highlight a tuner in red, give it a name, check the Enable for MCE box, and click 'Save'. Repeat for any other tuner. You can also change the names of the other configured tuner/s if you want.
(example pic1)

Now, you get to go in to the registry and set each tuner's recording and watch order. Otherwise, MCE won't use them.

1. Stop the Media Center Receiver Service (net stop ehrecvr)
2. Open Registry Editor (regedit.exe) and open this key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\MediaCenter\Service\Video\Tuners\{GUID}
where {GUID} is either {71985F48-1CA1-11D3-9CC8-00C04F7971E0} for Digital (HDTV) or {A799A800-A46D-11D0-A18C-00A02401DCD4} for Analog.
...

8. If this is the FIRST tuner:
RecordOrder = 0
RecordPrefered = 0xffffffff
WatchOrder = number of tuners - 1, e.g. for 4 tuners set this to 3
WatchPrefered = 0

If this is the LAST tuner:
RecordOrder = number of tuners - 1, e.g. for 4 tuners set this to 3
RecordPrefered = 0
WatchOrder = 0
WatchPrefered = 0xffffffff

If this is a tuner somewhere in the middle:
RecordOrder = whatever you put for the last tuner + 1
RecordPrefered = 0
WatchOrder = whatever you put for the last tuner - 1
WatchPrefered = 0

The idea here is that you increment the RecordOrder by 1 for each tuner, and decrement the WatchOrder by 1.  RecordOrder starts at 0 on the first tuner and goes up to #Tuners - 1; WatchOrder starts at #Tuners - 1 and ends at 0 on the last tuner.  RecordPrefered is true (0xffffffff) on the first tuner, false (0x00000000) everywhere else; WatchPrefered is true on the last tuner, false everywhere else.
9. Repeat steps 7 - 10 for each tuner, adjusting the values of RecordOrder, RecordPrefered, WatchOrder and WatchPrefered as appropriate.
10. Close Registry Editor.
11. Start Media Center. Voila!

I have 3 analog tuners and one HD. The ATI is tuner 1 and the other 2 analogs are off a Saber2020.
My ATI is set up to watch first and record last:
(example pic2)
My second tuner is set to record first and watch last. The last tuner is set in between.
(example pic3)
(example pic4)

MitchSchaft:

Now, you get to go in to the registry and set each tuner's recording and watch order. Otherwise, MCE won't use them.

Actually it will still use them.  The reason to set the orders is an attempt to control which tuner is used first.  MCE will also sometimes get a little confused because the tuners have the same priority levels so you get bad tuner warnings in history but the recordings still take place.

The only time this really matters is when you are using a stb with 1 or more tuners while not using a stb with a few more.