TCP packets don't flow from external hosts to WinVista clients behind nat

[Miz0]

Hello...
I've got a strange trouble...
FreeBSD 6.2 amd64 as nat-router:
rl0 85.249.249.249 -> ISP
fxp0 10.0.0.1 -> My Internat Net
natd/ng_nat
ipfw: allow all from any to any

WinXP client machines work fine behind nat, but WinVista, FreeBSD 
(5.5/6.2) clients don't.
It's very strange but it's unable to establish any TCP internet 
connection from non WinXP host. ICMP and UDP packets flows normally.
For example, I can ping host ya.ru, get DNS-reply from internet servers, 
play games via UDP, but i can't view web pages, open shh session and 
just can't "telnet" to any port!!!!
Traffic from/to my net is not filtering by firewalls at all. I've tested 
it with natd ang ng_nat - there's no difference! I've tried to solve 
this problem during last week =( Unfortunately, i can't. Now i'm going 
to try using pf or ipfilter instead of ipfw or ever reinstall server OS 
and may be change freebsd architecture to i386.

Any ideas ?
P.S.Sorry for my bad english.