These are two simple functions that I use on a daily basis to interact with a SharePoint List - Get List Items and Create a New List Item. The parameters for Get-SPListViaWebService are pretty straight forward. The URL is the URL of the SharePoint Web were the list resides. If a view GUID is not passed then the list items in the default view are…

Get SP List

function Get-SPListViaWebService( [string] $url, [string] $list, [string] $view = $null )
{
  begin {
		$listData = @()	
		$service = New-WebServiceProxy (Get-WebServiceURL -url $url) -Namespace List -UseDefaultCredential
		$FieldsWS = $service.GetList( $list )
		$Fields = $FieldsWS.Fields.Field | where { $_.Hidden -ne "TRUE"} | Select DisplayName, StaticName -Unique
		$data = $service.GetListItems( $list, $view, $null, $null, $null, $null, $null )
	}
	process {

		$ErrorActionPreference = "silentlycontinue"
		$data.data.row | % {
			$item = $_
			$t = new-object System.Object
			$Fields | % {
				$StaticName = "ows_" + $_.StaticName
				$DisplayName = $_.DisplayName
				if( $item.$StaticName -ne $nul ) {
					$t | add-member -type NoteProperty -name $DisplayName.ToString() -value $item.$StaticName
				}
			}
			$listData += $t
		}
	}
	end {
			return ( $listData )
	}
}

function WriteTo-SPListViaWebService ( [String] $url, [String] $list, [HashTable] $Item, [String] $TitleField )
{
  begin {
		$service = New-WebServiceProxy (Get-WebServiceURL -url $url) -Namespace List -UseDefaultCredential
	}
	process {

		$xml = @"
			<Batch OnError='Continue' ListVersion='1' ViewName='{0}'>  
				<Method ID='1' Cmd='New'>
					{1}
				</Method>  
			</Batch>  
"@   

		$listInfo = $service.GetListAndView($list, "")   

		foreach ($key in $item.Keys) {
			$value = $item[$key]
			if( -not [String]::IsNullOrEmpty($TitleField) -and $key -eq $TitleField ) {
				$key = "Title"
			}
			$listItem += ("<Field Name='{0}'>{1}</Field>`n" -f $key,$value)   
		}   
  
		$batch = [xml]($xml -f $listInfo.View.Name,$listItem)   

		$response = $service.UpdateListItems($listInfo.List.Name, $batch)   
		$code = [int]$response.result.errorcode   

 		if ($code -ne 0) {   
			Write-Warning "Error $code - $($response.result.errortext)"     
		} else {
			Write-Host "Success"
		}
	}
	end {

	}
}