Replacing suspension with a solid fork I have an older version of this bike: 


They have made some changes to the components since I bought my bike but it is more or less the same.  Here are the specs on the newer bike.  

I was hoping to put a solid fork on my bike for the winter.  I want to keep the mountain feel and have lots of clearance for wide tires, etc but I want to get rid of the weight and give my fork a rest.  

When choosing a solid fork what do I need to know?  


Will any solid fork fit onto my bike?  Do forks come in different sizes?  Different diameters?  Different lengths?  I heard something like you need a special fork if you are going to put it on a bike that was designed to be used with shocks.  
I know that I want a fork with disk break mounts so this makes the search slightly more difficult.  Ideally I would also like rack/fender mounts.  (For future touring).  
My wheel size is 26 inches, what would happen if I used a 700c fork on my bike?  This seller claims thats what he was using this solid fork for. 


Edit:

Thanks for the great information.  After reading I have been looking around for a used local fork.  I think that I found one possibility.  But any feed back would be appreciated.  


The fork was designed to be used with 700C or 29 inch wheels but it has an axel to crown length of roughly 17 inches (431 mm).  I currently have 100mm Travel in my suspension fork so Lantius says that I should get a fork with a length of 455 mm (17.9 inches).  Is this reasonable?  Does it matter if it was designed for a 700C tire if the fork length is correct?
As you can see in the picture of the fork the fork has some rake.  Is this a problem?  Will that amount of rake make the bike ride strangely/differently?
The steer tube/ headset size is 1 1/8th standard size which is the same as my bike so no concern there.  


Here is a picture of the fork:
It sounds like you've sorted out the first issue, headset size.  You'll need something with a  1 1/8" (also seen as 1.125" or 9/8") steerer.

Your bicycle's handling is based on the geometry. Changing the axle-to-crown distance will change the angle of your head tube, altering your bicycle's handling significantly.  The other major characteristic of a fork is "rake", or the distance that the axle is in front of an imaginary line down the center of the steerer.  Within 5-10mm of rake change you should notice a fairly minimal effect on the bike's handling, which is good because suspension fork rake is rarely published and measuring it directly is difficult.

The axle-to-crown distance is one factor, to get that right - assuming your bike has an equivalent fork - you should be looking for a "100mm suspension-corrected" rigid fork.  In practice this means a fork with an axle-crown distance of about 455mm.

If you want a 100mm suspension corrected, 26" wheeled fork with disc brakes that also has rack (I'm assuming you mean midfork low-rider rack mounts) and fender mounts, your options list is relatively limited.  The new Surly Troll Fork is likely to be one of your few options.