You can very well Deploy additional files like css, javascript or even an aspx page in SharePoint's 12 hive using your solution package's (or wsp's) manifest.xml.
Here are the steps you will follow for deploying a set of images in 12 hive's Layouts\Images folder.
1. Add a new folder "images" in your solution project and add images to it.
2. Add the below lines in your manifest.xml
<rootfiles>
<rootfile location="TEMPLATE\LAYOUTS\IMAGES\img1.jpg">
<rootfile location="TEMPLATE\LAYOUTS\IMAGES\img2.jpg">
</rootfile>
3. Add the below in your .ddf file to add these images in a wsp file.
.Set DestinationDir=TEMPLATE\LAYOUTS\IMAGES
images\img1.jpg
images\img2.jpg
and your done!