Policywonk:
BBC microsite 1358
Labour dismisses Alex Salmond's suggestion of a "progressive alliance", saying the possibility of the nationalists and Labour working together was "a desperate attempt by Alex Salmond to make himself look relevant after a terrible general election result".
... and yes, Gordon Brown could go to the Queen to resign as soon as arrangements were made for a govt. Until then, he remains PM - and I don't even think he needs to be head of the labour party to remain as such.
As long as the LDs know he's not there, and the new Labour leader is part of negotiations, I don't think there's a massive logistical issue.