Graphic files can be found under anims folder, from data.hpi and ipdata.hpi (this one comes with Creon updates).
You'll find 2 folders and a bunch of files: buildpic and weaponpic folders will have .jpg files which you can view easily.
Although, inside anims folder, the images are stored in .gaf and .taf format, they are mostly used in GUI and weapons, because of their ability to animate (like a .gif format). So, they will have sequences and stuff. For that, you'll need
GAF Builder Pro tool to deal with them.
Unfortunately, GAF Builder works only for .gaf files and not for .taf files. GAF files are used mostly in GUI, and .taf for weapons (I guess it's for their ability to have more quality).
In GAF Builder, you'll be able to extract the sequences as .bmp 24 bit format, and import .bmp 24 bit format too (and make your own gafs which will be referenced in data.hpi/guis or in an unit weapongaf and stuff)...
Well, good luck! If you need anything just tell.