Well, to answer my own question, here's a fix:
Read
http://www.killefiz.de/zaurus/showdetail.php?app=1012, download the patch for Intellisync, copy the DLL to your Intellisync install dir on windoze (backup and overwrite the existing DLL) and - yay! - alarms are set to "loud" on your Z when syncing next time with Outlook.
You will have to delete the datebook.xml on your Z and do a "fresh" sync to get rid of the old, silent alarms on your Z.
Peace,
Franky G