IPSec, is it possible?

[MK]

Hello

I would like to know if there is a way for traffic encryption between my 
computer, which is directed through my OpenBSD(NAT), to the internet.
My situation is following:

intranet ---- OpenBSD(NAT) --- internet

It is obvious that anybody on the intranet can sniff my traffic and of 
course I don't like it. I was thinking about IPSec, so traffic from my PC 
could be encrypted and then decrypted by OpenBSD and directed to it's final 
destination. But I think that in case of NAT it is not possible, am I right? 
I can not use IP address of intranet OpenBSD interface because the traffic 
will be directed to the internet hence this rule will not take place and 
encrypt my traffic. Maybe I could use some proxy on OpenBSD but I wanted to 
avoid similar solution.

Do you think I can accomplish my requirements without proxy?

Thank you very much for any hint.
MK