Has anyone ever heard of firewalls out there that block a TCP packet with a low "seq" number like "0" or "1"?

No. This is not considered a good idea due to older implimentations of TCP where the seq number started with 0. Many of these implimentation are still found in older computers.

I'm quite curious to ask why you think this is something you'd like to block?

Actually it's leads more to the question...why is my linux firewall spitting out sequence numbers that are very low...usually starting with 0, and 1 and so forth. I have 3 Slackware 9.1 linux systems all configured fairly similiarly. If I hook up my laptop, which is also running the same distro and kernel, directly to the cable modem...the sequence numbers look correct. But I just kinda figured that the linux kernel took care of the sequencing kinda automatically with some sort of hash routine or something.

This is all very confusing since I've tried various version of the new 2.4 series kernels and they all do the same thing with only this machine.