Ashish,
I have the exact same need (disconnected geocoding). I've been asking ESRI for this for years actually!
I was told that it was not possible with version 10 either, however there is a glimmer of hope that it may be: There is a sample that appears to use a local StreetMap SDC file for geocoding. I have not been able to get the sample to run, and I can find little or no documentation about the sample or Streetmap use within ArcGIS Mobile.
The sample is in "GeocodingTaskExtension.zip" located here:
C:\Program Files\ArcGIS\Mobile10.0\DeveloperKit\Samples\ApplicationFramework\Windows\
And is discussed very briefly in the Mobile Developer Help under the Samples > Windows Applications node. It's called "GeoCoding on StreetMap".
I think the StreetMap product is fairly expensive, but if in fact this works then it's a very good new addition under Mobile 10.