Most of this has been said, but I'll put in my 2 bits as well.
The best way to get into IPSC would be Production or Classic division.
For classic: Get a $350 Norcino 1911 (or any 1911 you wish) and a few thousand round of ammo and have at her. An Spartin or norc np-29 would be good if you decide you want to shoot minor and therefore shoot 9mm. But basically any reliable 1911 will do.
For production: Get any gun that's on the list and a few thousand rounds of ammo and have at her.
I shoot production with a Shadow and absolutely love the gun. It is pefectly ready to shoot IPSC out of the box, BUT if you decide you want to modify it almost any part is available for it and it will stay production legal.
Glocks, Sigs, Rugers(SR9), S&W M&P, would be the other popular production choices. All good guns, but Production legal parts aren't as plentiful. This doesn't matter if you like the gun as is.
And that leads me to this: as stated before, try every single last gun you can get your meathooks on! Fondle them ask question, and if possible shoot them. If you aren't comfortable with the gun it doesn't matter what gun it is, you won't shoot it well.
So while I highly reccommend a shadow, it's not the be all end all IPSC gun.
Then again it is so easy to shoot a rabbit can do it!(I've been posting this pic everywhere I go lately!)