Tiki strives to be useable by as many databases as possible. This is why we use the ADOdb abstraction layer.
The tracker you link to mentions Mysql 5 Alpha, not 4.1. Even so, I have increased the priority level.
I mentioned to Damian on IRC that lack of mysql 4.1 support is not a blocker bug for 1.9.0 We will look into this for 1.9.1 Please report any issues with Tiki 1.9.x & mysql 4.1 on dev.tikiwiki.org with as much detail.