VPN

I am wondering if it's possible to route certain or all WAN traffic through an IPSEC tunnel?  For example, Site A and Site B are linked together via an IPSEC tunnel.  I would like the users at site B to access the Internet (or a specific host) from site A instead of accessing it locally.

Make Sense?

As far as I know, not really.  It is to do with your 0.0.0.0 route.  Routing is quite simple when trying to get to a specific address it examines it's own subnet and if it is not on it, it passes the request to it's default gateway/0.0.0.0 route. For your internet traffic to go to the other site your router would have to have it's 0.0.0.0 route set to the other gateway which would mean that it wouldn't be able to maintain the tunnel.  Your best bet would be to use a proxy set up at the remote site and route your traffic through there.  Even better would be a proxy at each site with the site there being a downstream proxy.  If you are interested look at squid.