task bar

The answer is maybe.
Are you talking about the system tray, or the taskbar?
The tray contains icons for what used to be called TSR programs.
The taskbar shows active applications.

If you are asking about the tray, the answer is probably.
You can download tray managers from your favorite shareware/freeware site.
I know they are posted at annoyances.org, nonags.com and completelyfreesoftware.com
Some software won't let you disable the tray icon without disabling the software.

If you are trying to hide active applications, I don't know how to accomplish that.
You could make sure that the "hidden" app. is one of the last that you start, and stretch out the quick launch box to cause all open programs to hide.

If you write the application yourself, it is very easy to not have it diplay on the taskbar. In Visual Basic there is even an attribute for each form called ShowInTaskbar. Set it to false and you will only see the program in the process list. If youare trying to hide something from other uses, remember that the process list will also show what is running. Again, if you write it yourself you can also hide things from the process list that show when you hit Ctrl-Alt-Delete. It is not considered good manners to do so, but it can be done. Hiding things from the process list is much more easily done in Win 98 vs. NT or 2000.

As for an application that already exists, it would be very difficult to prevent it from showing up in the taskbar. This gets into the intercepting of windows messages at the Operating System level.

if you are programming the program yourself the answer is yes, you need to specif the programming language and learn how to do it in that language. if you are uisng