SharePoint Web Service Dataset Basics

More useful information:
The "GetListItems" function of the http://yoursite/_vti_bin/lists.asmx?wsdl SharePoint web service returns XML and you need to have this path to access the returned data:

soap:Envelope/soap:Body/GetListItemsResponse/GetListItemsResult/listitems/rs:data/z:row

The nodes involved (and therefore the path) will differ depending on which web service and function you are calling.

If you work with XML you'll understand nodes and how to decipher the path.
Logically, XML is simply nested data. the first node is soap:Envelope. Inside that is soap:Body, inside that is GetListItemsResponse, and so on.

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <soap:Body>
        <GetListItemsResponse xmlns="http://schemas.microsoft.com/sharepoint/soap/">
            <GetListItemsResult>
                <listitems xmlns:s='uuid:yourGUID' xmlns:dt='uuid:yourGUID' xmlns:rs='urn:schemas-microsoft-com:rowset' xmlns:z='#RowsetSchema'>
                    <rs:data ItemCount="X">
                        <z:row ows_FieldName1='FieldValue' ows_FieldName2='FieldValue'/>
                        <z:row... etc>
                    <rs:data>
                <listitems>
            </GetListItemsResult>
        </GetListItemsResponse>
    </soap:Body>
</soap:Envelope>

Tips:

• SharePoint prepends "ows_" onto the field names.  i.e. "Title" becomes "ows_Title".
• Any space in the field name is replaced with "_x0020_". i.e. "My Field" becomes "My_x0020_Field".
• Calculated fields return "string;#" before the value. i.e. a value of "Jimmy" becomes "string;#Jimmy" and you'll have to strip that or at least compensate for it before you use the data.

Here is a good post on SharePoint field naming conventions over at Web BorG.