Amongst other things at work today I was working on a gentoo linux http://gentoo.org server install. I always compile my own kernels, and downloaded the latest stable version (2.6.13.3) from kernel.org.
I found a slightly cut back version of the low latency patches I mentioned in the nextgen audio thread are now in the mainline kernel.
The patches are available here http://people.redhat.com/mingo/realtime-preempt/
What this means is pretty much every desktop targetted linux distro using >= kernel 2.6.13.3 is going to be fantastic for audio i.e. sub 5 msec latency.
When the experimental hard-realtime part of the patches are added to the mainline kernel this should go down to sub 1 msec.
Quite a bit more info about this stuff if available at http://aplawrence.com/Linux/kernel_preemption.html