2 Way speakers have the big woofer bit and a tweeter, 3 way have an extra "super-tweeter", which covers higher frequency.
3 Way may be best for the front of the car, but ony bother with 2 way in the back.
The Infinty are good, nice detail, but not exactly the last word in bass....
I would also recommend going for some components in the front and if you arent having a sub, then a decent set of 6x9s on a rear shelf. A reasonable 4 cahnel amp should do the trick - you can get a Sony/Kenwood etc for about £100 (Such as the KAC648 - £85 from CEL) Then something like the MB Quart DSD213 front components (£80) and MBQuart DTC169 6x9s (£85 from Caraudiodirect.com)
Spend the rest on cables etc and you should just about make it under budget, possibly buy a better amp if you can afford it.
My suggestion there, good kit, high quality and all for a good price.
Scott