I read an interesting blurb in the August 2009 edition of PC Magazine, which I thought was helpful. Here is an excerpt:

"Windows XP and Vista store the DNS information of websites you've visited, to reach those sites faster each time you access them. The cache sometimes gets corrupted or stores a lot of unusable data, and that leads to slower Internet response times. To clear the cache, go to the command prompt and type ipconfig/flushdns." - PC Magazine August 2009