I do a bit of home recording and I've been trying to set this up on my new Dell Studio 15 / Studio 1537 laptop. Latency is poor in the default set up, and there are cracks in the audio even if buffer size is increased. After going through the online forums it turns out the problem is in the ACPI driver in windows. Below is a solution that works for Windows XP 32-bit. Unfortunately 32-bit windows only recognizes 3GB of your 4GB ram. But that's an entirely different topic.
Method does not work on Vista (I tried on Vista 64-bit) - you'll get a message that says "Unable to access thread: The system cannot find the file specified." Running process explorer as admin makes no difference.
1. Download and run DPC latency checker:
2. Download and run Process Explorer
3. In process explorer, double click System.
4. Go to Threads
5. Select acpi.sys
6. click suspend
7. You'll notice that the red spikes are gone.
I would suggest re-enabling this before shutting down...