During fresh install (from CVS), MySQL says:

1101: BLOB/TEXT column 'sessdata' can't have a default value

ADOConnection._Execute(CREATE TABLE mdl_sessions2 (
sesskey VARCHAR(64) NOT NULL DEFAULT '',
expiry DATETIME NOT NULL,
expireref VARCHAR(25..., false) % line 891, file: adodb.inc.php
ADOConnection.Execute(CREATE TABLE mdl_sessions2 (
sesskey VARCHAR(64) NOT NULL DEFAULT '',
expiry DATETIME NOT NULL,
expireref VARCHAR(25...) % line 89, file: dmllib.php
execute_sql(CREATE TABLE mdl_sessions2 (
sesskey VARCHAR(64) NOT NULL DEFAULT '',
expiry DATETIME NOT NULL,
expireref VARCHAR(25..., true) % line 1899, file: dmllib.php
execute_sql_arr(Array[280]) % line 548, file: ddllib.php
install_from_xmldb_file(D:\Moodle\moodle/lib/db/install.xml) % line 179, file: index.php

This problem did not appeared on MySQL 5.0.33 and 5.0.22, and it seems to have a solution on http://moodle.org/mod/forum/discuss.php?d=58264#p267957