If there is a LR plugin for the forum (I haven't checked, but would be surprised if there is) then you could upload directly from LR to the forum. Otherwise you will need to export JPEGs from LR onto your hard drive and then upload them to your gallery.
Export as jpg with the appropriate size (I think 800 pixel on the long edge is the usual limit, but check), set the colour profile to sRGB and include the colour profile with the image so that those of us with clever browsers will see it correctly. Also include relevant exif data.
Then go to FM and create your post and point to the jpg on your drive to include it in the post. You will not be able to control where it appears in the post. That only works if you link to already-on-the-web photos.
As far as I can see there is no way to go direct from LR to FM .
Your profile says you have FM image upload , so the best way would to export at the settings you want to a place on your hard drive and then upload them to FM
If you want to send them to picasa I think you can go direct (i may be wrong as I'm not in front of my LR4 pc at the moment) if you can it would be much the same way I use for SmugMug.
I have collections under the smugmug part of the library . When you send your images to a collection you then publish and it uploads the images for you .
You set up all the upload options in advance and each upload service can have different upload options (my Flickr uploads have a different size and also have a watermark on them )
One other consideration. If you upload directly to FM there is a maximum file size limit. From time to time Fred has increased it, but I think it may be 650k. You can check the Upload page for restrictions. I typically export from LR as jpeg with longest edge set either to 1000 horizontal or 800 longest edge, max file size 600K, sRBG. Since you have the upload subscription you have the option of adding mat and frame, EXIF after upload.
Havent heard anything about a direct export to FM plug-in.
