Have a look at Monticello. It's a package available on SqueakMap 
(world menu -> open -> SqueakMap Package Loader). If you define your 
packages using the PackageInfo conventions

http://www.beta4.com/squeak/aubergines/docs/packageinfo.html

, you can then version them with Monticello. The Monticello wiki is 
here:

http://www.wiresong.ca/Monticello/

See the UserManual in particular. It has a tutorial that will get you 
started. There's also a mailing list where you can ask questions:

http://mail.wiresong.ca/mailman/listinfo/monticello