Here is how I burn my PS2 games, you may have to just keep trying till you get it right. I wasted over 25 DVD's while trying to get it right. So here are some instructions.

 I use DVD Decrypter http://www.dvddecrypter.org.uk/ and Alcohol 120 which is not a freeware program but here is the complete edition http://www.megaupload.com/?d=TS9PARH6

I use TDK and Verbatim media DVD-R. Some PS2's use DVD-R and others use DVD+R. You should check out your PS2 to see what you use. Once you get your ISO file use either software I use and burn it. Now here is the guessing till you get it right part. I burn it at 16x speed so I suggest you try that first. Other sites, actually everyone I went to for advice said to burn it at either 4x or 8x. Some suggest to burn them at half your media's MAX speed. What I suggest to try first is to burn them at MAX speed. 

If you get a MDF file and an ISO I advise to burn the MDF file with Alcohol 120 only, not DVD Decrypter. Again use whatever burning speed works for you.

If you have any questions or you're experiencing any problems I have a comment box at the bottom of this page to post any questions or comments you have.