Lightroom is setup as a Database to manage your images, with developing, printing, web output etc. as additional functions. It is not meant to be a raw converter just for selected images. If that is how you want to work, using Bridge and ACR may be a better solution for you. ACR and Lightroom have the same raw developing functionality with PSCS3. ACR ver4 is under the hood of Lightroom.
Normally with Lightroom photographers will import an entire group of images (or like me all of their images) then sort them, add metadata, and select the best shots for further developing and output. When additional editing is required files are best sent directly from Lightroom to Photoshop (without using Bridge) so the Lightroom database can keep track of them. You can send files to other programs too like LightZone for example, if you configure Lightroom for this.
There is no CS2 raw format. If you shoot Nikon, you have .nef files. Once you have installed Photoshop though, .nef files will by default get opened with ACR. You cannot double-click a file and have it opened by Lightroom. Files have to been imported by Lightroom first as they need to be in the database before further work can be done.
Lightroom is conceptually different than Bridge / ACR / Photoshop.