How else do I tell windows XP to display all active icons on the
taskbar when I already thought I had done so, by NOT placing a
checkmark on the " Hide inactive icons" checkbox on the taskbar
property window or page.

Hi, 

what you need to do is, select the Hide inactive icons check box, then
click Customize, then look at the Name column. One by one, select all
the icons that you want to show, and click Always show in the Behavior
column.

See, for example, these instructions for two sample icons:

Microsoft Windows XP official site
http://www.microsoft.com/windowsxp/home/using/productdoc/en/default.asp?url=/WINDOWSXP/home/using/productdoc/en/win_tray_taskbar_notifications_cust

omize_volicon.asp

Question: How do I add the volume icon to the taskbar?

To add the volume icon to the taskbar
Open Sounds and Audio Devices 
On the Volume tab, under Device volume, select the Place volume icon
in the taskbar check box, click Apply, and then click OK.
Right-click the taskbar, and then click Properties. 
On the Taskbar tab, under Notification area, select the Hide inactive
icons check box.
Click Customize. 
In the Name column, click Volume, in the Behavior column, click Always
show, and then click OK.
On the Taskbar tab, click Apply. 


AdSubtract.com's site
http://www.adsubtract.com/support.html
Question:  AdSubtract tray icon does not display with Windows XP.

Answer:  Windows XP 'hides' inactive icons. The appearance of the
AdSubtract icon tells whether filtering is active or not, so we don't
think it should be hidden. To prevent XP from hiding the AdSubtract
icon please follow these steps:
Right-click on the Taskbar 
Select Properties 
Select Customize to the Right of "Hide Inactive Icons" 
Double-click on "Hide inactive icons" in the Behavior column to the
right of AdSubtract
Select "Always Show" 
Click OK 

Thanks for your question!