Widimir wrote:

What I am really not sure is does anyone out there think that they made a difference on fighting in that kind of terrian?

Would the spear that native Germans used make that much of a difference?

It's fairly unlikely that their weaponry made a lot of difference. In the Germania Tacitus tells us that their spears were highly effective:

They carry a spear (framea is their name for it), with a narrow and short head, but so sharp and easy to wield that the same weapon serves, according to circumstances, for close or distant conflict.

But in the Annals he depicts Germanicus giving a different story about the unweildiness of these weapons in close combat:

"It is not," he said, "plains only which are good for the fighting of Roman soldiers, but woods and forest passes, if science be used. For the huge shields and unwieldly lances of the barbarians cannot, amid trunks of trees and brushwood that springs from the ground, be so well managed as our javelins and swords and closefitting armour.

This last passage has to be taken with a grain of salt, since it's fairly unlikely that warriors used to fighting in wooded terrain would be using weapons so difficult to weild in that terrain.

And it seems that it was a combination of tactics and terrain that gave Arminius the victory rather than weaponry. His strategy can be summarised as follows:

(i) Hide all indications of an impending uprising to gain the greatest possible suprise. Ambushing Varus while he was passing through what he though was friendly territory after luring him as far from his bases as possible was crucial to Arminius' success.

(ii) Divide the Romans' forces. By getting Varus to send vexillations to arrest wrongdoers in outlying settlements and guard strategic fords and staging posts, Arminius went some way toward reducing Varus' numerical advantage and gave his forces the chance to surround and eliminate these smaller groups once the rebellion was underway.

(iii) Attack the Romans on the march. Arminius knew from first hand experience that his Cherusci were no match for Varus' army in an open fight. He also knew how strongly defended Roman marching camps were. But he realised that a Roman army was most vulnerable on the march, especially if they were moving through friendly territory in peacetime and were relying on locals for scouting.

(iv) Use the terrain and weather conditions as "force multipliers". Dio tells us that the rebels used their knowledge of forest paths to use hit and run tactics - keeping the Roman column on the back foot and unable to co-ordinate an effective counter-attack. And the close terrain and foul weather conditions also worked to the Germanics' advantage. The fact that they were more lightly armoured and less enciumbered would also have made some difference, though Roman gear wasn't all that cumbersome. We do know that the rain caused the Romans' shields and their leather covers to become water-logged, which would have made them much harder to use.

(v) Use engineering works for the final blow. The Kalkriese excavations show that Arminius prepared the final killing ground for Varus legions in advance and used it to counter any final attempts at a counter attack or break out. Pinning the remnants of Varus' army between the forest on the Kalkrieseberg and the moorlands to its north, Arminius used his earthworks to retreat behind whenever the Romans counter-attacked. Already exhausted by three days and nights of fighting, this final tactic seems to have been the last straw.

Like all good generals, Arminius made full use of his army's advantages (local knowledge, fast movement, the advantage of surprise) and did everything he could to neutralise his opponent's, while exploiting his weaknesses. Despite being outnumbered and totally "outgunned" by a vastly superior enemy, he won a stunning victory as a result.
Cheers,
Thiu