Yeah, go through ticketmaster to find the presale link......the page for the date(s) you want will be the same as the one you would access through U2.com though....
Here's all the tips I can give you......
1) Only have one browser window open on a given computer....otherwise, it will just slow things down, and the second window will cancel out the first once it finds something....
2) When going for GA, simply select "GA" and "Floor Seats"......there's no need to put in the price range because if you select "GA Floor", it should automatically put it in for you when you submit.
3) Have a ticketmaster account in advance......you can store your credit card on there, etc.....it will save you lots of precious time.
4) Be very quick when it all starts.....keep refreshing the page with the ticket information (it should have a box that says "Tickets not on sale" or something).....keep doing that when you get near the time and be ready to submit your info once that area changes......after that, you have to type in a word that you see on the screen.....be swift!
4) If you get one GA instead of two (like if you only plan to go by yourself) your odds might be better.....I think this is due to the GA tickets being numbered, so the system would try to find two numbers together, even though it's pretty unnecessary......if you are going by yourself, your odds are better when going for one ticket.