I have no clue how to simulate the 'spikey head' effect of Darth Maul and need to.

Er, on an image? What program are you using? It's just a matter of painting some spikes onto the head. If you want to make it look good, be prepared to spend a lot of time on it.

No, I mean for a costume in RL to go to the opening day of episode 3 (that means I barely have any time left)

My friend dressed as Maul for the Episode One premiere. For the horns, he began with a set of custom carved styrofoam, but finding them hard to paint, sprang for a set of makeup horns at a local costume shop. If you have the money, do that. If you're on a budget, you can make them with mache or styrofoam, using maybe white glue to act as paint primer.

Buying premade horns is the best bet. And keep in mind that unless stuck to a skull cap over hair/skin, they will hurt like fuck coming off.

Why dress as Maul?

If I was going to dress up, it would probably be Fett or Vader.

Maul is a much more intricate and striking costume. It shows a level of dedication and draws a higher level of attention.

Fett and Vader outfits can be baught a second hand stores and dollar stores for Halloween costumes. As can Maul, but him wanting the horns means he is making his own, thus he must tailor the cloak, the gloves, the aforementioned horns, and of course, paint the face.

The face painting by itself takes several hours and is most impressive to behold in person, when done well.

Hmph, me and a friend are making costumes for Star Wars weekends, which should be starting sometime soon. He's making a Sith Master/StarFleet Commander, basically a Sith Dark Jedi with Imperial Insignia on his shoulders or chest area, and rank bars, and as for me, I'm making a Warlord costume. Zsinj style. I'm too fat for anything else, but not fat or large enough for a hutt. :D

I could wear a sheet over my head and be a Jedi ghost...

My super-geek detector just exploded.

omfg geeks