Populating share-point look up columns via the web service - sharepoint

Question

I am trying to populate a look-up column in a list, via the web service.
I am getting my data from an asp.net web form and using the web service method UpdateListItems and sending batch XML.
However, unless the user enters the exact data that the look up uses, the web service returns an error.
Is there anyway i can give the user of the web form, similar look-up functionality in order that the data passed will be identical?
i'm using share point 2007
The data source for the look-up column in share point is active directory.
_x0028_HR_x0029__x0020_Partner is the look up column, entering the users login name will look up their full name/ you can pick from a list.
Your help is much appreciated.
ClasService.Lists NewStarterList = new ClasService.Lists();
NewStarterList.Credentials = new System.Net.NetworkCredential(ConfigurationManager.AppSettings["SPUserName"].ToString(),
ConfigurationManager.AppSettings["SPPassword"].ToString(), ConfigurationManager.AppSettings["SPDomain"].ToString());
NewStarterList.Url = ConfigurationManager.AppSettings["SPUrl"].ToString() + ConfigurationManager.AppSettings["SPServicePath"].ToString();
try
{
string strBatch = "<Method ID='1' Cmd='Update'>" +
"<Field Name='ID'>" + clasStarter.ClasID + "</Field>" +
"<Field Name='Title'>" + clasStarter.Name + "</Field>" +
"<Field Name='_x0028_HR_x0029__x0020_Job_x0020'>" + clasStarter.JobTitle + "</Field>" +
"<Field Name='Entity'>" + clasStarter.Entity + "</Field>" +
"<Field Name='Practice_x0020_Groups'>" + clasStarter.PracticeGroup + "</Field>" +
"<Field Name='Dept'>" + clasStarter.Department + "</Field>" +
"<Field Name='Physical_x0020_Desk_x0020_Locati'>" + clasStarter.Location + ", " + clasStarter.LocationInBuilding + ", " + clasStarter.Department + "</Field>" +
"<Field Name='_x0028_HR_x0029__x0020_Line_x002'>" + clasStarter.LineManager + "</Field>" +
"<Field Name='_x0028_HR_x0029__x0020_Buddy'>" + clasStarter.Buddy + "</Field>" +
"<Field Name='_x0028_HR_x0029__x0020_Partner'>" + clasStarter.Partner + "</Field>" +//is a look up
"</Method>";
XmlDocument xmlDoc = new System.Xml.XmlDocument();
System.Xml.XmlElement elBatch = xmlDoc.CreateElement("Batch");
elBatch.SetAttribute("OnError", "Continue");
elBatch.SetAttribute("ListVersion", "1");
elBatch.SetAttribute("ViewName", ConfigurationManager.AppSettings["SPViewID"].ToString());
elBatch.InnerXml = strBatch;
XmlNode ndReturn = NewStarterList.UpdateListItems(ConfigurationManager.AppSettings["SPListID"].ToString(), elBatch);
}
catch (Exception exp)
{
throw new Exception("NewStarterForm - Clas Update failed ", exp);
}

Answer 1

I haven't figured out a full solution my problem, but i have figured out part of it.
Share point look-up columns have two parts, an id and a value. If you don't know the value then you can just use -1;# as a substitute for the ID
an example of this is
"<Field Name='Partner'>-1;#" + partnerLogOnId + "</Field>"
I will probably use a list, that allows users of my form to select people, and will pass the partnerLogOnId to my web service method.