1. Download the Apex Android 2.3 Gingerbread Themed ROM for Motorola Droid X
2. Copy the Android 2.3 Gingerbread Themed ROM for your Droid X to your SD card.
3. Make sure your Droid X is rooted. If it isn't, use the one click DroidXRoot tool to root it first.
Open Android Market on your phone and search for ROM Manager. Install the ClockworkMod ROM Manager app on your phone. Using this app, you can flash ROMs on your phone, backup and also restore your ROMs.
4. Open ROM Manager and click on the Flash Clockworkmod Recovery option to install the recovery image and backup the current ROM on your phone.
5. In ROM manager, use the Install from SD Card option. Select the ROM you downloaded earlier and flash it on your Droid X. Wipe the data and cache when flashing.
6. ROM Manager will upgrade your Droid X with the Android 2.3 Gingerbread themed ROM. You can now enjoy the Android 2.3 Gingerbread theme on your Droid X.

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If you have any issues with this new ROM, just go to ROM Manager and restore your old ROM using the Manage and Restore Backups option.
ROM Source: Droid X Forums
Download ROM: Apex Android 2.3 Gingerbread Themed ROM for Motorola Droid X