Lourna,
First, DON'T PANIC!!!!
The Standard looks daunting, but it is not quite a difficult as it seems.
First, do a comparison of the section 4 and 5.2 requirements to any documented quality system you have now (e.g. ISO 9001:2000, TL9000). Find the common elements and refer to them in your lab manual. That will save some time, and more importantly, you use an established base instead of reinventing the wheel.
Then you should be able to see the differences. In the lab manual, identify and address the requirements that are different for ISO/IEC 17025. One of note is Management Review, which in section 4.14 has a very prescriptive menu. You can and should add other parameters for review if appropriate for your business situation.
Now, you get to section 5.3 and following. That is the technical stuff. There are some sections (e.g. 5.10, reporting the results) where the Standard has common elements (5.10.2), test specific (5.10.3), and cal (5.10.4). Common elements of course must be addressed, as (for you) so must test specific elements. If you are not doing any of your own calibration, you can leave off the cal specific stuff.
Couple of points to watch. Your cal providers must be documented as being competent, having measurement capability, and traceability according to section 5.6.2.1.1. The easy way to accomplish that is use a calibration provider that is accredited to 17025 also. The hard way is to get a 17025 checklist and a Metrology professional, go to the cal provider, and audit them. Depending on their scope that could take several days.
Next point is measurement uncertainty (MU). Even as a test lab, you will have to do MU. There is another thread in this section that is better for MU questions.
Should you go for accreditation down the road aways, I also suggest shopping first, instead of centering on one or another of the accrediting bodies.
Hope this helps.
Hershal