To flash any custom ROM, you will need to have custom clock work mod on your Galaxy Tab 7.7. There are three different versions (i815, P6810 and P6800) and you can flash them via ODIN on your PC. If you do not have it on your computer, you can download it from this post – http://galaxytabreview.com/galaxy-tab-plus-official-us-firmware/ . Download the respective CWM for your Tab from the below given links and open ODIN. Here are the download links:
Select the file in the PDA field in ODIN and press the START button to start flashing of the CWM recovery.