I'm using a custom list-item-image in an "ul". However, the position of that bullet image is not the same as in IE and Firefox. Where is there a tutorial of a "hack" that makes the list item position consistent on both browser.

It would help if you would post some code to work with to assist you in finding a solution.

You get better control over the bullets if you have them as background images.

Example
li {
list-style-type: none;
margin: 0px;
padding-left: 12px;
background: url(../images/bullet.gif) no-repeat 0 0.3em;
}

Yep. Backgound image. That's what I ended up doing.

However, the position of that bullet image is not the same as in IE and Firefox

Yup, this is one of IE's many vagaries we all must deal with

I see Maxxximus gave you the right solution though