There's a preference setting for whether you want Camera Raw to open JPEGs in Preferences - Camera Raw.
Things in general become disabled (grayed out) if conditions aren't right for their use - for example if a selection is expected but not made, or if the image mode isn't one of those supported. Perhaps the quickest way for someone to judge what's not right is to put up a screen grab image showing the conditions when you expect the function to work,
ACR can be a useful tool with JPGs, but easiest with CS5 to use Ctrl/Cmd r from Bridge with the default for JPG to go straight into Photoshop.
Reasons FT is greyed out: You only have a background layer, or other layers are empty. The layer is locked. I can't think of any others. ???
Thank you so much. I worked it out and got it right yesterday.
Is there a basic pdf or video help available for Lightroom 3 which I have just loaded recently but have not used as yet?
When you reply by email you should disable your signature so your email is not posted in the forum. Regarding help for Lightroom - an Internet search will probably yield some good sources.
There are really good Lightroom training videos on Kelbytraining.com and probably lynda.com. They are not free, but in the end really worth the investment.
Edit: It is also a good idea to open a new thread with a descriptive subject line whenever you have a question not related to the original question in the thread. That way you attract readers who are knowledgeable about the subject matter of your question.