For anyone who is unsure on how to prepare and flash a custom splash1 image, allow me to paste here a step-by-step guide I posted on XDA:
TO BEGIN WITH, YOUR PHONE MUST BE S-OFF. FOLLOW INSTRUCTIONS IN THIS THREAD IF YOUR PHONE ISN'T S-OFF.
In order to flash your custom splash1 image, prepare a *.BMP image with size corresponding to your device's display size (which in case of the Desire is 480x800). Make sure the image is in 24-bit color space (true colors), 16 or 32-bit images wont work. When you have the image prepared, download a tool called NBIMG (you'll find it on XDA). Put your image and nbimg.exe into the same directory, open up command prompt and then navigate to the folder where you've placed the files. I'll use c:\nbimg as an expamle. To convert the image to the smartphone format, issue the following commands: chdir c:\nbimg
nbimg.exe -F mycustomimage.bmp -w 480 -h 800
This will create mycustomimage.bmp.nb file. If you want to be sure everything went alright, convert this file back to *.bmp format by using this command:
nbimg.exe -F mycustomimage.bmp.nb -w 480 -h 800
This will create mycustomimage.bmp.nb.bmp. Open this file and compare it to your original image. If the images match (no artifacts, inverted colors, etc.), you are good to go and you can proceed to flash the image to the phone using fastboot.
Take your converted image (mycustomimage.bmp.nb) and replace the .bmp.nb part with .img suffix so the resulting file is named mycustomimage.img. Now take this *.img file and put it to the tools subdirectory inside your Android SDK installation folder (fastboot.exe must be in said subdirectory, as I will use the path as an example).
Connect the phone to your computer and enable usb debugging.
Navigate to folder inside the Android SDK where adb.exe is located (older revisions of the SDK have it inside tools subdir, latest SDK has it inside platform-tools subdir). Reboot your device to bootloader mode through adb by issuing the following commands:
adb.exe reboot bootloader
When the phone reboots into bootloader, issue the following command to flash the image into the phone:
fastboot flash splash1 mycustomimage.img
Now reboot your phone using this command:
Enjoy your new custom splash1 image, you're all done :D
And if you let me, I'd like to share a few CM7 (maybe a little blasphemy here on MoDaCo B)) splahes I have created. They're nothing extra, just a quick and noobish work in GIMP, so if you don't like them, just don't download them and please, don't troll. I won't react on comments saying "your images are fugly" or anything else alike :P
Download the *.img files by clicking on corresponding images.
...or you can download md5sums of all the files above in a single *.md5 file here.