It happen to me a couple of times. Basically in Tortoise svn, you just need to add the password once and save it, it will keep working for months or years. In case I need to checkout another repository and it would ask the password again, it would be a nightmare.
But this simple tool helped- http://www.leapbeyond.com/ric/TSvnPD/
Download the exe file and execute it, it will pull out all the passwords saved for SVN.