This would be it in c# mate, i assume its simular in vb, but if I tried to do it in vb i'd get it all wrong :/
string user=Request.Form["UserId"].ToString();
string path="./upload"+user;
if (!Directory.Exists(Server.MapPath(path) ))
{
Directory.CreateDirectory(Server.MapPath(path);
}
Radupload1.TargetFolder=path;