It's actually really simple to catch latia/latios in Pokemon ruby/sapphire, assuming you still have your masterball. If not, find out about getting one from one of your friends or having someone with the emerald game clone you one, because without it it's a lot harder. First, put a Pokemon in the front of your party that is below level 40 but above level 35 (level 38 is good). Then fly to lilycove and buy a bunch of super repels (it's not worth it to waste your money on max repels; you only get 50 more steps, which you don't really need anyway). Strike out to route 121 and use the super repel before you step into the grass. This way, the only Pokemon that can attack you is level 40 latia/latios, because all the other Pokemon in the area are below level 30. If your super repel runs out before you encounter latia/latios, chances are it isn't in the area. So fly to lilycove again, becauseevery time you use "fly" it switches areas. Repeat the whole super repel-walk through the grass-fly to lilycove deal until you see latia/latios. When you do, just throw your masterball and voila! You have a super-powerful dragon Pokemon. If you don't have a masterball, you have to take one-shots and repeat the above steps over and over until it's weak enough for you to catch.
See related links for a walkthrough.
YouTube! Walkthrough
Go to Mimo77's blog. It has a complete walkthrough in words
just go on youtube and search for the walkthrough
To complete these missions you can go on youtube and type in what mission your on and it will give you a walkthrough.
by watching the walkthrough on youtube
Look up a walkthrough.
You can look on youtube.com and type in how to get the regis and there is a complete walkthrough on how to get there.
go to ign.com
you can get 1 when you complete your profile and you get one if you do the new walkthrough.
youtube it mate. find a walkthrough.
There are some walkthrough videos on YouTube. I also suggest going to IGN.com