According to http://help-pakistan.com/main/dont-block-the-blog/, the block has now been lifted.
See http://mail.wikipedia.org/pipermail/textbook-l/2006-March/002491.html for a press release forwarded to the Wikibooks list.
General information on blocks in Pakistan: http://pakistan.wikia.com/wiki/Internet_Filter_Status
http://meta.wikimedia.org/wiki/Wikimedia_projects_blocks still only mentions China.
Angela.