In version 4.4, you won't be able to see the flash in meg, your output will have something as follows;
Hardware: PIX-515, 64 MB RAM, CPU Pentium 200 MHz
Flash i28F640J5 @ 0x300
BIOS Flash AT29C257 @ 0xfffd8000
Flash i28F640J5 = 16 MB
^^^^^^^^^^^
you can determine how much flash you have with the following table;
i28F020 512 KB
AT29C040A 2 MB
atmel 2 MB
i28F640J5 8 MB - PIX 506
16 MB - all other PIXes
strata 16 MB
http://www.cisco.com/warp/customer/110/pixfaq.shtml#Q22
HTH
R/Yusuf