Url and permalink translation

Hello everybody,
I’m trying to move a wordpress to a new dir on the same web server and I’ve come across an interesting issue: a lot of visitors uses permalinks to access categories directly, like “http://myserver.org/myblog/mycateg/etc”. Now the blog is under “http://myserver.org/mynewblog/mycateg/etc”. Is there a way to translate automatically the base url to another one, a rule like “replace /myblog/ with /mynewblog/? I was wondering if this kind of redirection is possibile through a simple php script or not.

Thanks for any hints.