Take a look at some of the action shooting threads about getting started in IPSC. Here are a few tips to get you thinking.
1. What division do you want to shoot in? Production or Standard
2. Based on the answer to #1, chose caliber.
3. If you go production, and if you don't reload, go 9mm. 40 for production is OK if you reload, otherwise you will be shooting much hotter ammo than you need. Also, shooting 600+ rounds of full power loads in 40 for your Black Badge is a lot of pounding you don't need to go through.
4. If you go Production class, you will need a double action gun. Tupperware guns qualify, likewise the CZ and similar. Single action guns like 1911's are in Standard class.
5. If you go standard class, go 40, to make major power factor. Still helps if you reload (or buy reloaded ammo) for reduced power ammo for your Black Badge.
6. Now you can start narrowing down what gun you might want.
Also, read carefully the advice from jasonburnsdundee he is right on the money. If you know IPSC is going to be it for you, go for it.