Mipmapping is not used (e.g. effectively turned off for you) if your mipmap is not “complete”. Among other things, completeness requires all levels of the mipmap to be present, down to a map of size 11. If your code snippet above is complete, you are missing definintions for 88, 44, 22, and 1*1.
Hope that helps,
HM
[ October 30, 2004: Message edited by: Hans-Martin Will ]