Disable automatic capitalization in Office

You can enable or disable the various ways that the program automatically corrects capitalization.

1. Open Publisher document and on the Tools menu, click AutoCorrect Options.

2. On the AutoCorrect tab, select or clear any of the following check boxes as required:

Correct TWo INitial CApitals
Capitalize first letter of sentences
Capitalize names of days
Correct accidental use of cAPS LOCK key

However, to disable automatic capitalisation of first letter you have to clear Capitalize first letter of sentences check box.

For further information please visit the web link given below:
http://office.microsoft.com/en-us/help/HA101747301033.aspx#1