I'd recommend the Curt 12221. The key with a 2nd Gen GT is to make sure the hitch will clear the fascia on the bumper. The 12221 should clear just fine. The Curt 12234 will also fit, but would require some bumper trimming.
Also, as was said, unless the car is pristine underneath, the only thing you'll probably need to do is run a tap through the threads to clean them out first. I didn't have to on my Florida Vibe, but I surprisingly needed to on my Texas car. The threads were grody. I made my own tap from an extra bolt and cut slots down the threads with a Dremel. Worked well enough for a one time job.
2005 Vibe GT ~ Platinum
2006 Vibe ~ Lava, Base, Auto
2005 Corolla S ~ Silver Streak Mica, Manual (Wife's)
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete fools.