Convert xml (not standard) to html

Hi,

I request a web service to get a stream of xml whose content i saved in the attached file.
I have this content xml file . suppose i have this stream  saved into XML, and I create XDocument:  
XDocument doc = XDocument.Parse(xml);

 var user = from u in doc.Elements("a:string")
                                       select u;
When i run it, it has exception: ":" not allowed.

My goal is to get the u1,u3,u2,u5,u7 between <a:string>...<a:string>.



Since i got the data which is dynamic changing for different service i made a call.

Which approach i should use: using XSLT or LINQ via XML?

Thanks,
Tran
basicusers.xml