"lshw" will tell you. Sample output from my system:
Code:
description: BIOS
vendor: Phoenix Technologies, LTD
physical id: 0
version: ASUS A7N8X2.0 ACPI BIOS Rev 1007 (10/06/2003)
size: 64KB
capacity: 192KB
Also see libsmbios:
http://linux.dell.com/libsmbios/main/
This is supposed to implement smbios standard, though it may only work on dells right now.