A day back I was struggling to open a very huge file in eclipse and I was getting error, after browsing on net I found different answer and the one worked for me is here:
(I tried it in Lion I think it should work in other as well)
Go to finder:
- Select Applications
- Search for Eclipse folder and open it
- You will see different folder and files, one among them is Eclipse application launcher with eclipse icon.
- Ctr+click and select “Show package content” and you will see folder with name Contents
- Open it, you will see two files, select eclipse.ini, open it with your text editor
- You will see lots of information in it, the one you need for increasing heap size is “Xmx512m”, for me I doubled it “Xmx1024m” and now I can open huge files.
- Change it and save.
One can do it using terminal, but for novice these steps will be easy to follow. I hope it helps.
DreamPromt 
Thanks a lot!