Here are the two files that you are looking for...
Using the PPCGeeks kitchen (BuildOS), use the HTC_smart_mobility file for your boot splash and main splash. Enable the startup animation within the kitchen. Unzip and rename the SPCS_startup to wmstartup_ani.gif I attached to this post. I was unable to replace the wmstartup_ani.gif directly through activesync. Therefore, within the kitchen, I went into oemizer, selected files and shortcuts, and added my wmstartup_ani.gif file and created the oem. Once you create the oem, you must select it in the kitchen via a checkbox. It will say My Personal OEM. Build your ROM and it will automatically copy over the default animation with the sprint animation that originally came with the Mogul.