This is the script (You can also download it below):

$servers = ("BizTalk2010n1", "BizTalk2010n2")

#This function checks the status of the host instances on a BizTalk server ($Server).
function checkhostinstancestatusstarted ($server)
    {
    #gets all host instances on the server. Isolated (hosttype = 2) or disabled hosts are excluded .
    $hostinstances = get-wmiobject MSBTS_HostInstance -namespace 'root\MicrosoftBizTalkServer' | where {$_.runningserver -match $server -AND $_.hosttype -ne "2" -and $_.IsDisabled -ne "True"}

    write-host "Checking the state of all host instances on the server $server`:"

    foreach ($hostinstance in $hostinstances)
    	{
    	$HostInstanceName = $HostInstance.hostname

        #Checks the host instance state
        if ($HostInstance.ServiceState -eq 1)
            {
            write-host "$HostInstanceName`: Stopped."
            }
    	elseif ($HostInstance.ServiceState -eq 2)
    		{
    		write-host "$HostInstanceName`: Start pending."
    		}
        elseif ($HostInstance.ServiceState -eq 3)
    		{
    		write-host "$HostInstanceName`: Stop pending."
    		}
        elseif ($HostInstance.ServiceState -eq 4)
    		{
    		write-host "$HostInstanceName`: Started."
    		}
        elseif ($HostInstance.ServiceState -eq 5)
    		{
    		write-host "$HostInstanceName`: Continue pending."
    		}
        elseif ($HostInstance.ServiceState -eq 6)
    		{
    		write-host "$HostInstanceName`: Pause pending."
    		}
        elseif ($HostInstance.ServiceState -eq 7)
    		{
    		write-host "$HostInstanceName`: Paused."
    		}
        elseif ($HostInstance.ServiceState -eq 8)
    		{
    		write-host "$HostInstanceName`: Unknown."
    		}
        }
    write-host `n    
    }

foreach ($server in $servers)
    {
    checkhostinstancestatusstarted $server
    }

<#
Service states:
Stopped	1
Start pending	2
Stop pending	3
Running	4
Continue pending	5
Pause pending	6
Paused	7
Unknown	8

See: http://msdn.microsoft.com/en-us/library/aa577472.aspx
#>