The splash-screen in After Effects and Photoshop is in fact PNG-files wrapped in a resource .dll-file. This is a common way to hide resource-files in both programs and games.

Of course I don't recommend you to do this... This is just information for how it is technically done...

Modified version of the Photoshop-splash:

It could be done like this:

1. Download "Resource Hacker" - the no.1 tool for this job.
2. Unzip the program to a suitable location, no installation is needed.
   
3. Run Resource Hacker.
4. Locate the resource file:
   PS: C: > Program Files > Adobe > Adobe Photoshop CS3 > PSArt.dll
   AE: C: > Program Files > Adobe > Adobe After Effects CS3 > Support Files > AfterFX.dll
5. Copy the file to the desktop.
6. Rename the original to .old (PSArt.dll  --> PSArt.old), giving you the chance to revert your mistakes. IMPORTANT!!!
   
7. Open the file in Resource Hacker, and roll down the PNG-option.
   Locate:
   AE_SPLASH or SPLASHARTBACKGROUND.PNG (Photoshop). (There are many versions of this resource, depending of your version of Photoshop).
   
8. The PNG is coded as binary data, to hide it a bit more for us guys. Select the "1033" under the AE_SPLASH and choose
   Actions > Save Resource as a Binary file...
9. Save the file as splash.png (only the .png is important).
10. Edit the file in Photoshop.
11. Merge your layers and save the file(still PNG).
12. Reenter Resource Hacker and right-click the 1033 - choose:
    Replace Resource...     (AFTER EFFECTS)
    
    
    Replace Resource...     (PHOTOSHOP)
    
    Notice that the resource-type is PNG for AE and PNGF for Photoshop.
13. Choose File > Save
14. Copy the AfterFX.dll or PSArt.dll to the program-folder.
15. Start PS or AE to see if it works...  Enjoy!

One modified file will not work on every installation, only the exact same installation...