If you are using Photoshop CS6, a patch has been released that enables it to open the a99 RAW files, you can simply open the program and use the auto update function and you're set. If you are using Lightroom 4.2 an update has also been released for both the Windows and Mac versions, sadly the Windows version is only available for 7 or Vista and not XP.
For the rest of us processing the Sony a99 RAW files requires more effort, because Adobe will not provide Camera Raw support for older versions of their software (obviously trying to get people to pay to upgrade to the latest versions), instead we will need to use additional programs open or convert the files first. I think the best program available right now is the DNG Converter 7.2, which is made freely available to download by Adobe (how nice of them), you can download it by following the links below
Windows version (the program will also run on Windows XP)
This program will convert the RAW files into DNG files, which can then be open by pretty much any programs. The only hassle is that converting does take sometime, but since it will convert a whole folder at once you can leave it to do it's thing while you go grab a cup of coffee or something. Another downside is you will need extra storage space for both the original RAW files and the converted DNG files.