Surely you can change the LinkSys to perform as a Access Point, not a router/gateway. If you can, simply:
adsl--->e-smith-->hub (or X-Over)-->linksys-->WLAN
I've got a Compaq CPW2 and it'll let me choose to either be a router/gateway or a wireless access point. Hopefully Linksys will provide you the same functionality, else you will end up with a double-NAT configuration.
Internet->E-Smith-->[NAT]-->LinkSys-->[NAT]-->WLAN
Which would be pretty inefficient and redundant. Possible problem-prone as well.
Hope this helps,
Nathan