The latest CVS snapshots will allow you to update them directly, without
having to download a new snapshot. Just unpack the archives, go into the
SDL directory and run “cvs -z3 update -d” whenever you want to get the
latest and greatest SDL development code.
SDL 1.0:
http://www.devolution.com/~slouken/SDL/cvs/SDL-1.0.tar.gz
SDL 1.1:
http://www.devolution.com/~slouken/SDL/cvs/SDL-1.1.tar.gz
Keep in mind that CVS code may be broken at any given time. If you want
the most stable source possible, wait for the periodic public releases.
I plan to release SDL 1.0.6 tomorrow… Yay! 
See ya!
-Sam Lantinga (slouken at devolution.com)
Lead Programmer, Loki Entertainment Software–
“Any sufficiently advanced bug is indistinguishable from a feature”
– Rich Kulawiec