I was thinking of a good weapon vs undead, namely Skeletons, obviously a Mace of Disruption came to mind. Then I began wondering if you could also have a Bane of Undead on there as well to stack or does the Disruption itself count as a Bane and therefore not be able to have both? and if you can have both would it work like on your first attack you hit and enemy saves so they get hit with the Bane 2d6? (note: usually play 3.5 but may have to switch to 4.0)
I have absolutely no idea how magic items in general work in 4e, much less how bane or disrupting specifically work, but in 3.5 they are separate properties that can be applied to the same weapon.
Bane is a +1-equivalent, and disruption is a +2-equivalent, and you need to have at least +1 real enhancement bonus on a weapon, so the cheapest you can combine the two is with a +1 undead-bane mace of disruption (or whatever other base bludgeoning weapon you wanted), which is a +4-equivalent weapon. You pay 4²×2,000 gp = 32,000 gp for the magic, 300 gp for the masterwork quality, and 12 gp for the mace, for a total of 32,312 gp.
When attacking an Undead creature with this weapon, you would gain a +3 enhancement bonus on both attack rolls and damage rolls, +2d6 damage, and force a DC 14 Will save vs. destroying the creature.
In D&D 3.5, yes, you can add both Bane and Disruption to the same weapon. Note that while the disruption enhancement refers to it as 'the bane of all undead', the two bonuses are not in any way alike, so we can assume this is simply an oversight. However, as KRyan mentioned, the fact that you need the weapon to have a +1 base to apply special enchantments to it means it will require a +4 weapon at the minimum, making it quite expensive. It seems unlikely that disruption, in particular, will be terribly useful by that level with its rather impressively low DC 14 save.
In D&D 4e, this is strictly not possible. Each magical weapon may have one and only one special property (though you may have a weapon which is simply 'magic' and has no special properties outside the extra to-hit and damage). This is one of the many ways in which 4e attempts to streamline play and promote balance, for better or worse. On the positive side, since special properties in 4e are an assumed part of the weapon, they often scale quite well with level.