The Germans in WWII did not have enough vehicles, especially armour throughout the entire war. During the invasion of Poland in 1939, machinegun armed training tanks had to be used on the front lines. Fortunately for the Germans, the Poles didn't have much in the way of effective anti-armour weapons and their tanks were little more than toys spread thinly across the country.
The German reputation for good, powerful and well armoured heavy tanks was not justified until the later part of the war when the Tiger, and later the Panther came into being. Until then, they were using whatever they could scrounge to suplement their relatively meagre production of Pzf III's and IV's of various models. Even so, their heavy tanks were never available in great numbers and suffered from overly complex mechanicals and less than ideal production values (hard to keep quality high while your factories are being bombed).
It also has to be remembered that Germany had been prohibited armour following WWI, a prohibition they secretly (to begin with) flouted, and the declaration in 1932 that they would no long abide by the Treaty of Versailles.
http://en.wikipedia.org/wiki/German_...n_World_War_II
http://en.wikipedia.org/wiki/Treaty_of_Versailles
Beginning from a standing start, Germany had no choice but to use whatever weapons, vehicles and equipment they captured. (They could of course have chosen a less warlike course, but with the Nazi's in charge that was never going to happen.)
There were some examples in WWII of Allied units using German equipment, but these are VERY few and far between.
After the war many countries, especially those directly occupied by the Axis had to rebuild using whatever came to hand. This was a very different situation than we see in the first few years of WWIII.