Hi Wentsi,
The easiest way to do this is by using the Import/Export feature. Go to Customize > Integration Tools and click on Go to Import / Export. Click on the radio button to the left of Export a table to a file, uncheck the checkbox to the right of Show only common tables?, and select the CustomerType table from the dropdown list.
Next, uncheck the checkbox to the left of all fields except for the Name field, so that your screen looks like this:
Make sure the radio button to the left of Comma-Separated Values is selected, then go ahead and click the Export to file... button at the bottom right of the screen.
Open the file in Excel or whichever program you'd like to use to edit it, and remove all of the entries except for "Name" (which should be at the top of the list). Then go ahead and add any options you'd like to have in your Customer Type dropdown, each in the next cell down from "Name". You should wind up with something that looks like this:
Save that file somewhere you can easily access it and go back to Customize > Integration Tools > Go to Import / Export... in Method. This time click on the radio button to the left of Import into a table from a file, uncheck the checkbox to the right of Show only common tables?, and select the CustomerType table from the dropdown list. Click on the Choose File button and select the file that you saved in the last step. Then click on the Import data... button at the bottom right of the screen.
On this next screen, leave everything as it is (Vertical, First Row is List of Field Names, To Existing Field) and make sure the field name "Name" is selected in the drop down list. Click on Import Data and on the next page click Begin Import. After the import completes, go ahead and edit a customer to verify that your new options are available.
Hope this helps.
- Justin