When you get an xml result from the SharePoint webservices, these results are Strings, but in the SharePoint dll these results are availbale in an enum.

private SPFieldType GetFielType(XElement xElement) {
return (SPFieldType)Enum.Parse(typeof(SPFieldType), GetAttribute(xElement, AttributesWeb.Type));
}

I created some wrapper classes that makes coding easier against SharePoint Webservices, in time I will publish more of these:

these can be found here