Creating folder with timestamp in name

I'm creating a console application that moves files to an archive after a certain number of days. Within the archive folder, I want the application to create a folder that has a time stamp within the name i.e archive_20110725, so i can easily navigate to a certain days outputs. Here is my current code


using System;
using System.Configuration;
using System.IO;


namespace FileArchiver
{
class Program
{
static void Main(string[] args)
{

var pollingDirectory = ConfigurationManager.AppSettings["PollingDirectory"];
var archiverDirectory = ConfigurationManager.AppSettings["ArchiveDirectory"];
var fileRetention = Int32.Parse(ConfigurationManager.AppSettings["FileRetention"]);




foreach (var fullFileName in Directory.EnumerateFiles(pollingDirectory))
{
var fileInfo = new FileInfo(fullFileName);
var fileName = Path.GetFileName(fullFileName);


if(DateTime.Now.Subtract(new TimeSpan(fileRetention,0,0)) > fileInfo.CreationTime)
File.Move(fullFileName,Path.Combine(archiverDirectory,fileName));
}

}

}
}

Thanks for any advice,

Josh

.NET4.0 / VS 2010 btw

What's the problem?

string filename = String.Format("archive_{0:yyyyMMdd}", DateTime.Today);