Is there any example, tutorial, paper or swiki page about how to serialize instance objects in Squeak ?
This might be much more sophisticated than what you are looking for:
http://wiki.cs.uiuc.edu/CampSmalltalk/Binary+standard+for+object+interchange
Simpler alternatives are available in the Squeak image itself. Look at the classes in the category "System-Object Storage".
ImageSegments (see the class comment) are very interesting, but the simpler SmartRefStream might solve your problem.
-- Jecel P.S.: nice to see some more Smalltalking in Brasil