'Dose anyone know if it safe or ok to try to install into my g3?' - Insert the 'DVD' disc (unless you really have the set of 'Tiger' CDs - which you would then insert 'Install Disc 1'), and reboot the G3 Mac with the 'option' key pressed. If the DVD is displayed within the list of boot-able volumes - there is a good chance that the installation is possible.
'Like if i install it and it freezes or something i can still boot to my 10.3.9 that is already on it?' - no. You should however back up your currently working operating system, and related application installations, onto another hard disk drive - using '
Carbon Copy Cloner' (freeware), '
SuperDuper' (freeware / shareware), etc. Only then you can return the internal hard disk drive to its former (working) state - should the recent 'Tiger' installation attempt fail.
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The above reply is based on the assumption that you currently have 'Tiger' installed on the G3 Mac, and require re-installation of the operating system - and have access to another persons' 'retail' 'Tiger' installation disc, due to the inability to locate your own 'retail' 'Tiger' installation disc.