When creating tools, you may need to create custom icons. MicroStation is now Windows compliant, and is able to use *.ico's as Windows does. Another option would be to generate a bitmap outside of MicroStation, then use the bitmap image for your icon. Either way you will need to generate the icons outside of MicroStation.
If you plan on creating just a couple if icons, you can use something like Microsoft's Paint program. But if you plan on creating several hundred icons, you might want to consider purchasing an icon editor to do this.
Open the user tool you wish to select an icon for, as listed below on the user tool for "linear dimensions". If you look at the lower section where the properties are (under the general settings) you will see the current icon being used for this tool. There should be a browse button next to the actual icon.
This is the dialog that opens for your selection of an icon for this tool. The "User Selected Icons" will allow you to browse to your operating systems icons.
Here are "User Selected Bitmaps". These would be bitmaps generated by you from another program, such as Microsoft's Paint.
Along with this list are the MicroStation icons from its' own resource. This is one that was picked for this example case.
In this case we selected the "construct array" icon from MicroStation's resource to be used for our custom tool. Here is the end result.
Customizing tools and tool boxes in MicroStation