Defeating the Zolom at first encounter is actually pretty easy if you know what to do.
I defeated him at level 14 or something like that. I also got beta.
If you just want to kill him, just enter the fight with Barret, and make sure you have the "Mind-Blow" limit break. Use it, and the Zolom will loose all its MP in a single blow, and won't be able to cast Beta, which turns the fight into a pretty straight forward brawl where you just need to keep on healing and attacking.
Using Matra Magic enemy skill, and limit breaks should do the trick.
You can also manipulate how the Zolom knocks people out of battle.
The Zolom will knock people out depending on which ones do the most damage to it.
If you have a character you don't want knocked out, just make sure that character isn't attacking the Zolom until it has knocked out the two other characters.
Also, to lessen the damage the Zolom deals, put all your characters on the back row, and have them induced with the "sadness" status effect using tranquilizers.
If you want Beta, just have one character, preferably Barret (since he has mind-blow), equipped with the elemental effect materia paired with a fire materia, and of course with the "sadness" status effect as well as the enemy skill materia. Also have as few magic materia as you can on him (just fire and cure) to avoid his HP decreasing too much.
Keep Barret from attacking, using him only as the healer, and when the others are knocked out of battle, start the offensive until it casts Beta. Heal, and then use Mind-blow to stop it from doing it again.
Then alternative between attacking/using magic attacks and healing until it dies.
It's relatively simple.
After having cleared Gold Saucer and gotten the manipulate materia, and having a second enemy skill - I went back to the main continent after having gotten Big Guard, then got White wind, and then went back to the Zolom to get Beta again.
When you have Big Guard and White wind, pluss the extra levels, it's even easier.
So essentially, you'll have two Beta enemy skills before even reaching Cosmo Canyon, which makes the rest of disk 1 a cake-walk.
You're welcome =P