To stop Windows from changing the case of your filenames to upper or lower case:

Start Regedit
Go to HKEY_CURRENT_USER \ SOFTWARE \ Microsoft \ Windows \ CurrentVersion \ Explorer \ Advanced
Double-click DontPrettyPath (or create this key with a type of REG_DWORD if it doesn't exist)
Set the value to 1 to keep the case as you type it or 0 to adjust the case as Explorer requires
Click OK
Close Regedit