A communications breakdown between the pilot and ATC resulted in a descent to a lower altitude that triggered an ATC low altitude alert.

Narrative

On ILS 2C at BNA; I was being vectored to the localizer. Well prior to intercept; I was reassigned the ILS for 2R. I was given descent instructions and vectors to allow for faster traffic. I remember being given instructions to turn heading 020 and descent and maintain 2;000. This could be in error but this is what I recall. I questioned the heading only; as it didn't make sense (parallel to the localizer course but several miles east of it); but didn't question the altitude; and read back 2;000. Upon reaching 2;300 FT; I received a low altitude alert; and I was instructed to climb and maintain 3;000. Non-rated passenger stated immediately after this call that he also heard the controller assign me 2;000. No EGPWS terrain warning was triggered.In hindsight; I should have recognized that 2;000 was too low for both approaches; whether this was assigned by the controller in error; or I readback the wrong altitude. I did note that the published GSIA for ILS 2C was 2;500. However; I had not fully briefed ILS 2R given the unexpected switch and unusual vectors. Frequency was very congested; and it sounded like 2 controllers; one overriding the other.