I also just bought a Nixon Comp. Here are some tips I have learned after talking with Manitou service techs and reading the service manual on the Nixon.
1. Setting Sag: None of the Nixon coil forks (Comp & Elite) come with a provision for preloading the spring to fine-tune sag. Your options here are limited to selecting the proper spring for your weight. I would suggest calling Manitou to determine this as I don't remember seeing a chart anywhere with this info. Adjusting the compression dial on your fork will do nothing for setting sag. On the TPC damper in your fork the compression adjustment is for low-speed compression. Adjusting this will affect how the fork reacts over small to medium sized hits and can help to control pedal-bob to a degree. Here is an "under the table" tip that the Manitou tech would not officially confirm due to liability: If you decide you would like to fine-tune the sag by preloading the proper spring for your weight, you could make some small spacers to stack on top of the spring. This would require threading the top cap on under pressure as you push down on the spring and spacer. Be very careful not to strip the threads. My idea was to buy some PVC pipe with an outside diameter just smaller than the inside of the stanchion tube and maybe throw a nylon washer between the spring and spacer for good measure. Make sure that the PVC wall thickness is such that it contacts the spring and top cap fully. The spacer would not need to be very large to fine-tune your sag measurement. It would be a process of trial and error. I had been planning to go through this process with my fork. I purchased the recommended X-Firm spring for my 230lb weight and found that the 1" of sag achieved with no preload was less than the 1.4" (25% of travel) that I was shooting for. I am, however, able to hit the bottom-out bumpers through the course of my regular riding so I am inclined to think that a lighter spring with pre-load spacers to fine tune my sag would be sprung much to lightly. From what I've read in this forum the general consensus on Manitou coil forks (especially the Nixon) is that they are undersprung. I believe it has more to do with the dampening than with the spring-rates provided by Manitou (more on this in my next point).
2. TPC Tuning: For my tastes, the TPC damper on the Nixon Comp works fine for casual trail-riding but is overtaxed when the going gets rough (this may have something to do with my weight). The low-speed compression and rebound dials have a small adjustment range that is nearly invisible once you hit the trail. With my old Fox Vanilla fork the adjustments made a visible difference from max to minimum settings (with the Rebound set on max the fork extended much slower than with the Rebound set on mimimum). Right now I have my Nixon Rebound set on max and the extension is still not being controlled to my liking. In addition to the limited adjustment range, the fork blows through its travel much too easily (rolling on flat ground I need only to hit a small 4" bump while simultaneously forcing my weight down on the handlebars to nail the bottom-out bumpers). This is not a case of being undersprung but rather the TPC damper is not progressively controling the fork's motion as it should. The only possible solution here is to put a heavier oil in the damper. The TPC comes stock with a 5wt oil. The Manitou tech I spoke with recommended using a 7wt or a 10wt oil in my situation. This should make the Rebound and Compression adjustments more effective and should help to better control the forks movement under fast compressions.
3. Change Damper: The best thing about Manitou forks is the wide range of configurations you can use to set up your fork. Coil Sprung: travel adjustable or fixed (for lighter weight as in the Nixon Comp). Air Sprung: IT travel adjustable or fixed. Dampening: TPC, TPC+, SPV Evolve, Intrinsic. With these combinations you should be able to change your fork to perfectly suit your needs. In my case I am waiting for the TPC+ damper which is now available in the '06 Nixon Elite (the guys at Manitou said production should be moving along shortly on aftermarket dampers). The TPC+ damper adds a floating compression piston to the standard TPC unit. The floating piston is pushed against the adjustable compression piston under high-speed impacts. This is said to increase the dampening and in effect provides the progressive compression control under sharp impacts that I am looking for.
Those are the three suggestions I have for tuning your Nixon Comp (change and fine-tune the spring, tune the TPC, or change the damper). In my case I had been planning to change the TPC oil to 10wt to try and better control the fork's adjustments and high-speed dampening. I have since left it alone as I am waiting to purchase a TPC+ damper to which I will probably add the 10wt oil.
P.S. I hope you bought your Nixon Comp from Jenson as I did. They have been offering it for $199 from time to time. The secret is that these particular forks at Jenson have aluminum steerers rather than the standard steel you normally see on the Comp (Jenson said that this is simply how the bike company that they bought them from had them speced from Manitou). So for $199 dollars you can buy this fork, order any available Nixon parts (air spring, travel adjuster, damper) you desire and still be hundreds of dollars under the prices that unsuspecting buyers are paying for '06 Nixon forks!