If the lid close causes it to hang, then acpi is sending a signal to the kernel upon lid close as it should.
However the machine may be told to enter a hibernation state which Linux does not handle very well causing it to freeze.
Since this seems to be working DO NOT disable ACPI, rather fix the problem.
You have to modify the behavior of the machine when it receives an acpi signal for lid close.
I set mine to merely blank the screen on lid close and perform a shutdown on a tap of the power button (I don't have a Dell though...).
To do so I modified the acpi configuration entries.
and change what follows
... to what you want your machine to do when the lid is closed.
ACPI is also required to enable your multimedia keys (once you get your sound running this is important!).
You can install ACME
(if you have properly set up your URPMI sources http://www.zebulon.org.uk
Now you can set the multimedia keys to do what they should do.