you cnat wire two dual 4 ohm subs to get a total resistance of 2 ohms. you can get a total of either 1, or 4 ohms.
you can wire them like so:
each sub parrallel to 2 ohms each, then together in parrallel for a total 1 ohm load.
each sub series for 8 ohms each, then together in parrallel for a 4 ohm total.
here is a great link on wiring subs:
http://www.crutchfieldadvisor.com/S-...rs_wiring.html