this is the case, I'm using Backtrack 5 R3 64bit live from USB flash. LAN cable goes from computer to Access Point (TPLINK WA500G), and from AP goes coaxial cable to grid antenna.

Wired connection is good, it says its connected and I can access AP in browser and look for networks around (in browser), its fine, but when i type "iwconfig" output says something like this (i'm on windows now so i cant copy paste):

lo no wireless extensions
eth0 no wireless extensions
wlan0 mode managed... // irrelevant, thats wireless card which i dont want to use.

and airmon-ng recognizes only wlan0 as wireless.

is there a way to make eth0 usable with aircrack? is it a driver issue ?

Welcome to LinuxQuestions.

AFAIK no. Aircrack is designed to use wireless adapters in monitor mode. Since the wireless functionality is being performed by the access point they are unavailable to the connected computer.