I ask as i kited a Mammoth to whiterun as i needed a tusk i thought ill take it near a guard tower and they will fire in some arrows for me aswell (being on master at lvl7 is a pretty long haul to kill a mammoth solo and hopefully it will stay this way!) and the Guards...well...did nothing at all.

I heard them shout ''aaah a fight!'' or something then they just looked on at me kiting this mammoth towards the first Archway gate so im safe from the one hit kill....(mammoths cant fit through there hehe) eventually i killed it after 88 arrows and using my weak destruction magic of sparks and flames ><

so has anyone ever had a Guard help them? (not including inside city Dragon Attacks)

Actually outside of Dragon attacks I'm not sure I have.

hmm strange i wonder if this is intended or perhaps is a bug?

Yes. I'm doing a no-kill game now and I've led bandits and wolves near the watchtowers outside of Whiterun where the guards take care of business for me. The ones walking near the meadery tcb too.

Where to get the mammoth tusks:

Maybe they recognize a fight that they can't win and stay away.

I've had city guards attack a dragon I was fighting once. And like you I kited 2 giants and 3 mammoths to Whiterun. The guards helped with the giants and I used the terrain of the boulders to keep the mammoths at bay. The giants can't duck under the guard towers by the way, so you'll stay safe. Like you I to use low level when I did this.

Well oone time as I was at Darkwater Crossing this stormcloak on guard pulled an axe on me, so I pulled my dagger on him for an epic staring contest. Eventually he said "If its a fight you want, its a fight you'll get," and him and his pals started slaughtering all the civilian miners. Only instance I've had of guards attacking anything besides the first dragon and a couple of bandits near Lorius farm.

I was attacked by some thugs in the middle of Windhelm before and the guards simply ran away.

No, the guards are dumbasses and refuse to help my character. Sometimes at low levels I need help and run into town with whatever is with me in tow. The guards just yell "I'm staying out of this!" or "I'm getting out of here!" They won't help with a few bandits or a bear but they'll help kill a dragon.

I had the ones at Darkwater Crossing help with a mammoth and a couple of sabre cats.

My thief character was attacked by thugs just outside of Riften before. being a thief i was not very strong so died fairly quickly. After a reload I tried to run towards the guards, hoping they would help, and despite one of the thugs actually hitting a guard with a fireball, the guards did nothing to help me.

Guards do indeed help out. I`ve used them several times and not just against Dragons.

Was just leaving a village when after a short run was attacked by 3 Thalmir (I think they are), the elves in gold and a wandering Troll who wanted a piece of the pie. They were blasting at me with ice spells. I ran back to the village where the guards duly despatch them all. I was a little worried they might kill the guards but I helped out by archering the enemy.

Yup, guards in Ivarstead saved my scrawny thief butt from a bear (thar's b'ar in them thar woods!) just last night. It's a long way to Riften and my stolen horse had run off when I dismounted to mug some unwary travelers.