UO Flddler thread
I know this thread says it's for animators, but that's just because they enhanced the animation interface.
UO Fiddler is the standard tool for the majority of modders.
You might have to look around for it, but I believe there's a tutorial about adding art to your client with UOFiddler.
But basically you go to the Items tab. Right click in the sprite field. Enable Show Free Slots. Everything red is open. Find a good place to add your custom art (I always like to keep everything I add close together if they're all similar type items). Left click to select the square (it'll chance color and display the properties in the right column). Then right click the square again to pull up the menu. Select Replace and it'll ask you to choose the image file to replace with. And that's how you add a graphic.
And once you have all your graphics imported, I'd recommend that you save the files (yes, it does take a while). It saves the files Art.mul and Artidx.mul. I BELIEVE it saves them to the default MyDocuments folder somewhere but you also have the option to save them elsewhere...which I always do and why I can't remember where the default location is. Then exit UO Fiddler.
When you find them move them back to the client folder (yes to overwrite...though make sure you've made backups of all your files before modding....that's just generally a good rule)
But that's not all. Start UO Fiddler. NOW it will load with the new graphics which makes these next steps easier.
Find your graphics. Right click on the first one. Click Select in TileData tab (a bit of a wait). And click Select in RadarColor tab (also a bit of a wait). Jump to the TileData tab and your item should be shown. These are the general game properties. FIRST, in the upper left corner there's a Misc menu item. Click that and make sure the "Save directly on changed" option is checked....this might slow down editing the properties a little but the alternative is jumping back up to Save Changes every time you've finished a graphic...and I've forgotten to do this before and had to go back and redo everything I THOUGHT I just completed.
Hopefully you've found a tutorial about adding art so I don't have to cover what all these properties are....but they should also be somewhat clear.
*Note* a few of these graphics are intended to be animated so remember to check the Animation box for them.
Once you've finished with these, Save Tiledata....this just saves a file called tiledata.mul.
Then you jump to the RadarColor tab. Again, your item should be shown. This is how the graphics look on your radar. They show black unless you choose otherwise. Easiest is to pick the Average button. This is just the average color in the graphic. You have other options too...but I don't generally mess around with that unless I have something specific in mind...like I'm trying to conceal a "No Show" wall meant to block boats from passing so I give it the radar color of water...or like I'm adding a bunch of land and I want it to look the same on the radar.
When done, just Save File...which saves to a file called radarcol.mul.
Exit UO Fiddler and move these two files back to the client folder.
A few of these were animations....so open UO Fiddler again. Yes...I know it's a lot of save, exit, move and reopen but it needs to have the current data. You'll figure out the routine after a while and won't think about it anymore.
You need to jump to the AnimData tab.
You know what...this DOES have a tutorial. A shame it appears that the screen shots (if there were any) have disappeared.
Animation tutorial
Hope this helps!