Hello All.
I know that there are quite a few guys here running the XPS 420, so I just thought I'd share my overclock findings, as they seem to be few and far between out on the Internet.
I had found an article (home.austin.rr.com/waterdogs2/xps420.htm)outlining a method of overclocking called a "BSEL" mod, which used a Permatex Rear Window Defogger Repair Kit liquid metal to jumper the BSEL pin to another on the Q6600 processor. Supposedly this would allow your Q6600 that normally runs at 2.4GHz and 1066FSB to run at 3.0GHz and 1333FSB.
I also found an article (http://www.ocforums.com/showthread.php?t=546760) that showed how just covering the BSEL pin with a couple tiny pieces of electrical tape would achieve the same performance increase.
Going by "The simplest fix is the right one" philosophy (theory), I did the tape mod and VOILA! Using CPU-Z I measured the stock speed going up to 2.4GHz, and after the mod I am getting 2.995-3.033GHz! 1333FSB! Those speeds are only showing when I am doing something and CPU-Z shows a multiplier of 9x, but when the system is idle, the Intel Speedstep Technology takes the multiplier down to 6x, reducing the speed to 1.995GHz. Like I said, though, whenever the computer is doing something productive it jumps up to 3GHz, so I think I'll leave that alone, as I don't mind running a little cooler when idle.
I understand that a couple of users here have used the first method, I just wanted to make a formal post with the how-to links as I had to search high and low to find them.
I hope you have as good of luck as I have! This probably voids your warranty... so proceed with caution.
Jake
EDIT: I received my XPS 420 on 4/29 from the Dell Outlet and here are the specs: Q6600/3GB 667MHz RAM/ATI HD2400 128MB.