I recently bought a DS and have not played a pokemon game since the Silver/Gold days.

I remember back then there were differences between the paired up versions.

SO was wondering which is the better choice out of Diamond and Pearl?

Diamond -

Dialga
Mime Jr.
Skunky
Skunktank
Cranidos
Evolved Cranidos

Pearl -

Palkia
Bonsly
Glameo
Purgley
[Triceratops pokemon, forgot the name]
[evolved form of triceratops pokemon...]

Those are the only differences Pokemon wise that I can remember. The story is the same on both. Gameplay is also the same. I think on pearl the menu's may look a bit more colorful and pink. Not sure about that though. Ask someone else.
If you pick either tape you'll get the same experiences, and there is trading over wifi globally, so you don't really have to worry about getting the other pokemon from the other tape.

Sorry If I spelt any of the pokemon's names wrong...

EDITED.

wait platinum.

I just bought Pearl becaues my roomate had Diamond. He convinced me to buy the game after I had given up on pokemon XD!

It really doensn't matter what game you get. As long as you know someone who owns the other or have wifi, you should be find. It all depends on who you thinks is more awesome--Dialga or Palkia.

Diamond. Dialga looks so much cooler than Palkia, and that's all that matters.

If you can do that [doesn't have a release date] then that works to.

If you dont want to wait for Platinum buy Pearl, a lot more people own Diamond than Pearl

Yeah, depends on what you're interested in.
I hear that Platinum is going to have a bunch of extra content, just like what Yellow was to Blue and Red, what Crystal was to Silver and Gold and Emerald was to Sapphire and Ruby. That's what I'm waiting for myself.

Personally, I'd go for Diamond. I've always had a preference towards the blue spectrum, and indeed, there is also the point where it's less girly than pearls, but as has been mentioned, I have a feeling most people go that route, so it's much harder to find people who have Pearl.