How to downgrade packages recursively?

[Krzys Majewski]

Can I use apt to downgrade packages? How? 
For example, I set my sources  to point to "unstable" because I wanted
libsdl1.1, but apt-getting libsdl1.1  resulted in a libc6 upgrade that
broke some other  stuff. The only way I could  find to downgrade libc6
(and all the  other packages that were upgraded along  with it) was to
manually d/l the debs, and dpkg -i them. -chris