[AT&T Samsung Galaxy S II SGH-I777] dayv:
The first thing here is to know what you have flashed already and what kernel you want to be running (putting the kernel you want on will be the last step and only part that may need adb depending on which kernel - will cover those steps in another post or via pm)

Bella92108 i just re-read your posts and looks like you are stock plus rooted kernel. Abacon15 it will work for you as long as you are similar or on one of the att sgs2 based rom's such as dg's cognition or gtg's unamed. If you are on cm7 or some varient, it can still be done as well, but you may have to reflash cm7 by the time all is said and done, and if this is the case just pm me instead of going forward with this and I help with that if i can.

1st step. Go to entropy512's Return/Unbrick to stock here http://xdaforums.com/showthread.php?t=1286432 and download his kernel + rooted system package - while there click his thanks button for putting these packages together for us.

2. Once downloaded we need to extract the contents of the package - if osx is like linux here you can just double click the package and your archive software will popup with the option to extract the contents, if so just do that. Once you have this extracted you should have a PDA.tar file.

3. Now we need to extract the contents of PDA.tar, just like the step above open with your archive software and extract the contents. Once extracted you should now have a zImage file and a factroyfs.img file. For the rest of the way we only need the zImage file - flashing the factoryfs.img would reset you to the factory app package that came with the phone and remove all your installed apps, could be useful to you in the future, but not what we want here.

4. Open your terminal and navigate to the same directory/folder where we have extracted the above zImage file (zImage is the kernel by the way if you did not know). If you don't know how to navigate in terminal one option is to just move the above zImage file to your home folder with you gui file manager (if osx is like linux) because when you first open terminal in linux it automatically opens to your home folder. To make sure we are at the right place in terminal where the zImage file is enter terminal command

ls

The output of this command will list all the files and sub-folders that are directly in the current folder and if we are in the right place here you should see our zImage file in the list.

5. At this point put your phone into download mode and connect to your computer.

6. enter into terminal the following commad

heimdall detect

Heimdall should detect your device here and if it does then move on to the next step, if you get a warning like "heimdall failed to detect compatible download-mode device" then we have a connection problem to fix first.

7. To flash the kernel enter command

heimdall flash --kernel zImage

If you get a good flash and your phone reboots you should now be rid of the triangle exclamation point warning on the initial boot splash. If you get a permission error then we need you go back and run your terminal as admin, or use the sudo command in terminal if that works in osx just like it does in linux as follows

sudo heimdall flash --kernel zImage

it should as for your login password here again if it is like linux

At this point if all has went according to plan we will be ready to flash what ever kernel you would like to be running. Just pm me here and let me know what you would like to be running and I will help you through the steps for this as well, it may or may now require adb, if it does that is not any harder than what we have done so far.