Vista - NAnt / <XMLPOKE> and xpath question ...

Hi,
I have a simple exe.config issue where I'd like to swap out the config
file with NAnt/XMLPOKE. I just can't figure out the correct xpath to
get to the "file=" attribute.

I want to swap in "US, UK, ..." depending on the target regions.

Thanks,

Craig
===========================
my exe.config file:
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<appSettings file="Dev_custom.config">
....
....
</appSettings>
</configuration>
===========================
XMLPOKE tasks that don't resolve to the "file=" attribute correctly

<xmlpoke
file="${configFile}"
xpath="/configuration/appSettings[@file='incorrectFileName']/
@value"
value="US.config" />

<xmlpoke
file="${configFile}"
xpath="/configuration/appSettings[@file=@value]"
value="US.config" />

<xmlpoke
file="${configFile}"
xpath="/configuration/appSettings[@file]/@value"
value="US.config" />