Sorry for english (there is no Russian here)

Where can i find the information about hyperkaehler structures
on T^*GL(n,C), T^*GL(n,C[z]/z^n) ?

Motivation: these manifolds are T^* to moduli spaces of vec. bundles
on singular rational curves (up to small detail).
Kapustin-Witten use essentially the hyperK. str. on T^*BunG.
If one wants to understand what is going on there
it seems the best toy model to start.