Your cards are 100Ghz compliant (which also happens to make them 200Ghz compliant). The delination really comes into play when you purchase the DWDM filter equipment. The ITU wavelength grid for the C Band is comprised of 40 wavelengths spaced at 100Ghz. Most manufacturers simply omit every other wavelength from thier equipment design when putting together a 200Ghz system and some even have add-on modules to the coupler/filters that allow for a 200Ghz initial deployment with an optional upgrade to 100Ghz spacing. Whichever you decide to go with, the coupler/filter sets will dictate which wavelengths are available to you when looking to purchase additional optical line cards (such as GBICs or XENPAK).Since you only have 1 wavelength currently deployed, you are not currently commited to either 100Ghz or 200Ghz as of yet. I recommend pricing out the DWDM coupler/filters, amplifiers, and OADM equipment you may need for 100Ghz so that you do not limit your future scalability as the price differential these days between the two is negligable.
One last note... Make sure you do proper loss budgeting and if you are using amplifiers or OADMs Wavelength power calcuations (if the equipment doesn't do it automatically) for the DWDM system. The conversion from a linear transport to DWDM gets more complex the more distance you add to the system.
