Neither the reason you deleted Mail nor the reason you want to use it now make sense. Anyway, you can reinstall Mail as described here:
Custom installs in Mac OS X 10.4
If the version of the system software on your installation disks is earlier than what you're using now, then you must also reinstall the corresponding Combo Update afterwards, to bring the Mail application back in sync with the rest of the system:
Mac OS X 10.4.7 Combo Update for Intel
Also, you may want to read the following articles for guidelines on how to properly install system updates:
Troubleshooting installation and software updates
Installing software updates
Basically, you should verify/repair the startup disk before installing the update, and no applications should be running while installing it.