Got a way to make it so immortals don't suffer from lag?

Make them all live together in the same house as the server.

Get them all broadband, get a decent connection for the server.

It works for me ;-)

More seriously lag is a product of:
1: Slow connection from server to internet
2: Slow connection from user to internet
3: Overloaded servers
4: The internet

Unfortunately only points 1&3 are under your control, 2 is in the hands of the user and 4 is down to the whims of the internet.

On a brighter note we have sorted out what we can and its very rare that 4 is a problem - I am on broadband and if my commands don't respond instantly then I consider it laggy...

Yeeh, that is an entirely mudlib dependant question!

Without knowing what sort of driver/mudlib etc you are using then we can't do any more than guess.

Find the section of code which causes the mortals to wait and make it conditional on whether you are an Imm or not.

Personally I don't like the idea of locking people up like that though - the way we do it is that spells can take any amount of time to cast and don't block commands, but certain commands (like casting another spell or moving) will abort the spell.