I have not skined in almost 3 years back then I had maya 5 and a plug-in that let me select the verts and choose the influence that each joint held on the verts so it was as easy selecting the verts and giving both joints 0.5 influence over them
now tho I cant find that plugin and even with (hold) on if I replace to .50 influence it just randomly asines some thing like .2 to random joints !!!
I swear that the skining technology needs a overhaul it has always been a really lame time sink(for me any way I hate it with a passion)
any way is there dose any one know a plug-in the lets you select verts and set influence As_skinny says it dose but it dosnot do it in the way I want it more for copying weights