Before stopping the SharePoint services, it's probably worth running the following to see what state they are in (e.g. running, stopped, etc.):

Get-WmiObject Win32_Service | Where-Object {$_.Name -eq 'ssosrv' -or $_.Name -eq 'dclauncher' -or $_.Name -eq 'dcloadbalancer' -or $_.Name -eq 'osearch' -or $_.Name -eq 'spsearch' -or $_.Name -eq 'sptimerv3' -or $_.Name -eq 'sptrace' -or $_.Name -eq 'spwriter'} | Format-Table name, state, status -auto

To stop all the services related to SharePoint 2007, simply run the following PowerShell commands on the services you'd like to stop:

Stop-Service ssosrv
Stop-Service dclauncher
Stop-Service dcloadbalancer
Stop-Service osearch
Stop-Service spadmin
Stop-Service spsearch
Stop-Service sptimerv3
Stop-Service sptrace
Stop-Service spwriter

And to start them again:

Start-Service ssosrv
Start-Service dclauncher
Start-Service dcloadbalancer
Start-Service osearch
Start-Service spadmin
Start-Service spsearch
Start-Service sptimerv3
Start-Service sptrace
Start-Service spwriter

If you wanted to be a bit more clever about it, and not get any error messages if services are already stopped/started/disabled or not installed, you could use:

function StopIfStarted([string]$ServiceName) {
    $Service = Get-WmiObject Win32_Service -Filter "name='$ServiceName'"
    if (!$Service) {
        # Service is not installed
        Write-Host "$ServiceName is not installed on this machine."
    } else {
        # Service is installed
        if ($Service.State -eq "Running") {
            if ($Service.StartMode -eq "Disabled") {
                Write-Host "Cannot stop service $ServiceName as it is disabled."
            } else {
                Write-Host "Stopping service $ServiceName ..."
                Stop-Service $ServiceName
            }
        } else {
            Write-Host "$ServiceName is already stopped."
        }
    }
}

StopIfStarted "ssosrv"
StopIfStarted "dclauncher"
StopIfStarted "dcloadbalancer"
StopIfStarted "osearch"
StopIfStarted "spadmin"
StopIfStarted "spsearch"
StopIfStarted "sptimerv3"
StopIfStarted "sptrace"
StopIfStarted "spwriter"

and:

function StartIfStopped([string]$ServiceName) {
    $Service = Get-WmiObject Win32_Service -Filter "name='$ServiceName'"
    if (!$Service) {
        # Service is not installed
        Write-Host "$ServiceName is not installed on this machine."
    } else {
        # Service is installed
        if ($Service.State -eq "Stopped") {
            if ($Service.StartMode -eq "Disabled") {
                Write-Host "Cannot start service $ServiceName as it is disabled."
            } else {
                Write-Host "Starting service $ServiceName ..."
                Start-Service $ServiceName
            }
        } else {
            Write-Host "$ServiceName is already running."
        }
    }
}

StartIfStopped "ssosrv"
StartIfStopped "dclauncher"
StartIfStopped "dcloadbalancer"
StartIfStopped "osearch"
StartIfStopped "spadmin"
StartIfStopped "spsearch"
StartIfStopped "sptimerv3"
StartIfStopped "sptrace"
StartIfStopped "spwriter"

These script files are attached.

To see which services are running, you can use:

Get-WmiObject Win32_Service | Where-Object {$_state -eq 'Running'} | Format-Table name, state, status -auto

Note:

Microsoft Single Sign-On service = ssosrv
Office Document Conversions Launcher service = dclauncher
Office Document Conversions Load Balancer service = dcloadbalancer
Office SharePoint Server Search service = osearch
Windows SharePoint Services Administration service = spadmin
Windows SharePoint Services Search service = spsearch
Windows SharePoint Services Timer service = sptimerv3
Windows SharePoint Services Tracing service = sptrace
Windows SharePoint Services VSS Writer service = spwriter