VLAN, Linux, and raw sockets

I've read the VLAN HOWTO and a few other resources I could find on the 'net and I'm left wondering how to do what I need.

I'm working with a 2.4.18 kernel.  (Yeah, I know it's old, but it's stable.  From what I can tell, that's new enough to have VLAN support.)  I want to write a VLAN-aware program that sees and reports on all VLANs on an interface.  It seems to me that means opening a raw socket through which I can see all messages on an interface (regardless of VLAN tag) either with the VLAN tag intact (and I'll process it myself) or with the VLAN tag for a message available via some ioctl or something.

However, everything I see suggests that to do VLANs, I'd open my socket on "eth0.42" or something and see only traffic destined for VLAN 42 on interface eth0.  Am I wrong, am I missing something?  Can I open a raw socket and get all traffic on an interface with VLAN tags intact?  Anything to get me started would be welcome.

                             Chris