Make sure both the major and minor tick mark types are indicated on the Patterns tab of the Format Axis dialog box.

You indicate that you want more marks between your present minor tick marks.  If I understand correctly that would be three levels of tick marks - Major, Minor and Sub-minor(???).  If that's true - you've got me.  I'm only aware of two levels of ticks.
 

You only get two levels so you will have to change the scale of your minor tick marks if you want more.

Unless there is VB access to these that i don't know about.

Remember...
       "If you don't use your head,
                       your going to have to use your feet."

bpage77:

You can only have two types of tick marks... major and minor.  To get the minor tick marks to show up, double click the axis (y or x axis) and select the "Patterns" tab.  In the "Minor Tick Mark Type" box, select anything except "None".  This will make the minor tick marks visible.  To set the minor tick mark spacing, click on the "Scale" tab and next to "Minor Unit" enter the spacing (100 for your given example).

Good luck!

jproj