Fixing media links after importing to multisite

Question

When i imported all posts and media from a old site to new site which on wordpress multisite. The image links on posts are got broken because how media are stored on a multisite is quite different from a single installation wordpress site. And also the links in the contents are static so it don't change when imported.

Single installation example:

http://oldsite.com/wp-content/uploads/2010/07/image.jpg

Multisite installation example:

http://mysite.com/files/2010/07/image.jpg

So, you see if i can go through all posts replace old links with the new links in all image/media links it is going to work. We need to change the first part of the url. the name and the date of the media will be same as the importer will use the same publish date and name when imported.

My question is:

Is there any plugin which can do that? or some other way i can do it?