Gaps between menu items - difference between IE7 and Firefox

[pdmsuser]

Hello, hope someone can help. I have a problem with the spacing between the menu items. If an LI does not have any sub menus, then the IE7 hack below works and gets rid of additional white space. However, this does not work if the LI has a sub UL element. I need to take out the extra spacing as this does not show in Firefox and I would like to set a reasonable margin width between the menu items that is the same on both IE7 and Firefox.
#udm li a {display:inline-block;}
#udm li a {display:block;}

Does anyone know if there is anythign I can use that will take out the white space on menu items that have sub menu items.
Thanks