Copy the file kbdcr.dll from another (Croatian) Windows XP computer to your folder c:\windows\system32 (or expand from an original Windows XP CDROM)
Open regedit and navigate to HKEY_LOCAL_MACHINE\ System\ CurrentControlSet\ Control\ keyboard layouts and search for kbdcr.dll (0000041A on my machine, when I Google it says 00020405 for Croatian keyboard layout, but I found Czech/programmer in this folder)
now edit the Registry Key HKEY_CURRENT_USER\ keyboard layout\ preload, change the "1" value setting to the matching key from HKEY_LOCAL_MACHINE\ System\ CurrentControlSet\ Control\ keyboard layouts (e.g. 0000041A)
Done and Dusted!
(Note: Preload\2 is used if you want to be able to switch between two keyboard layouts.)