Paypal issues

[jmestep]

We have a client who is having trouble with paypal and there is a limit to what we can troubleshoot since we can't access his paypal account and he had some settings wrong in the past.
I've looked at this forum thread:
viewtopic.php?f=42&t=8894&st=0&sk=t&sd=a&start=0

and this help doc:
http://help.ablecommerce.com/mergedProj ... paypal.htm

which says it needs WSE, but the info on the forum posts see a little confusing.
On installing WSE, the help file says:

You should install WSE 3.0 before installing AbleCommerce. However, if you need to install WSE 3.0 after AbleCommerce is installed, then you will need to backup the web.config file and replace it when finished.

Does the installation of WSE on the server make changes to the web.config file? When the docs say we need to backup the web.config and replace it, what do we replace it with?

Thanks