hey i also wanted to know if my party in diamond is any good 
Kyogre Lv. 100   Groudon Lv. 100  Salamence Lv. 100  Zapdos Lv. 80
Hydro Pump       Fire blast             Fire blast                Thunder shock
Sheer Cold         Fissure                Dragon claw            Thunder
Surf                  Solar Beam          Double-Edge            Charge
Thunder            Eruption             Fly                          Drill peck
Giratina Lv. 70   Regigigas Lv. 70
Shadow force   Confuse ray
Heal block        Stomp
Earth power     Superpower
Slash               Zen Headbutt
Hey macdaddy, here's a few suggestions for your party. I am not an expert or anything, but I battle against people sometimes. I can only give a few at the moment for time issues, but I'll try to pop in for a few more when I get off work.
As Caterkiller said, if you want to win in game, that's probably a good team to have. However, if you want to play against competitive pokemon players, you need to make some adjustments. 
First, your party consists of three pokemon that are considered uber in most pokemon circles: Kyogre, Groudon, and Giratina. You would have to focus on either having a team with all ubers (or non-ubers who can stand on their own in the uber world), or get rid of them in favor of other pokemon. Ubers are usually legendary pokemon that have huge stats. Ubers, for example, are Mewtwo, Mew, Lugia, HoHo, Deoxy, Latias, Latios, Kyogre, Groudon, Rayquaza, Darkrai, Dialga, Palkia, Manaphy, and Arceus. Some people also consider Garchomp uber, but I personally don't.
Another thing to think of when forming a team is to make sure most of your team doesn't have a common weakness. For example, your team would have problems against a hail team, or a team that used a lot of ice attacks. I think Zapdos, Salamence, Giratina, and Groudon are all vulnerable to ice attacks. If someone had a powerful enough Weavile, he could tear your team to pieces. I'd say try to have a team that shares at most two type weaknesses all around. 
Another quick suggestion would be to get rid of attacks that overlap with each other, or take two turns to use (Except Solarbeam in some cases, and hyper beam for PorygonZ). For example, three of the four attacks your Zapdos knows are electric. If a Jolteon or Electrivire came out, you could only use Drill Peck, or else they would absorb your electric attacks. The only exceptions would be to have two type moves that functioned in different ways. Magnezone can have thunder and thunderwave. Thunder would be used to attack, and thunder wave for status effects. 
Also, most tournaments have rules against moves that one hit KO pokemon.