is it possible to mod guns in OB?

Possible yes. I don't think however it would fit in well with the rest of the world there nor with the lore

Yeah, Besides

that kind of modding would require much more work than anyone would want to pursue for the sake of a cheap thrill

I thought it was impossible becouse of lack of crossbows?

well you still have bows, so you could still have the launching-action but you might have to mod a lot more now then you would in morrowind.... to get a gun I mean, which I think is dumb.

its for a zombie mod that is not in any way related to Tes.

If I was trying to mod a gun into Oblivion (which I don't intend to do ), I'd start with the magical staffs rather than bows. My understanding is that they're going to be cast-when-used, charge-based, rechargeable from soul gems, point-and-shoot affairs that go in your weapon slot and are triggered by the attack button (rather than the spell casting button). So, change the graphics of the staff into a gun, change the graphics of the soul gem into an ammo clip, and change the FX of the spell that the staff casts into something less magical-looking, and you're well on the way to something gun-like.

i changed my mind, the mod will not have guns, but it is still not related to Tes.

Well I'm sure someone will come up with a way to mod in crossbows as well

i never liked crossbows, i like to stick to my trusty steel bow.