You will be unable to switch SIP keyboard using EzInput when using the stock WM Sip menu. All that is displayed is "EzInput". When I used my Fuze, I had this issue. Even newer HTC builds don't have it working.
The only way you can get it working is by using a biotouch.dll that turns the SIP menu into one of the HTC menu kind. Only the HTC Sip menu will allow you to change your SIP Keyboard.
Myself and others have actually started using a Manual SIP changer app that will open this "HTC Sip Menu" and allow you to switch... but you have to run the app to do it. You can't do it on the fly.
I've created a thread about this already in the Dev forums where I've been dissecting a few of the EzInput packages and was getting pretty far when I had my Fuze replaced with a Pure.
Even my Pure (topaz), running WM6.5.1... the SIP menu is one of HTC's designs. If I disable this menu... all I get is "EzInput". I really wanted to get a stock SIP menu that would work but eventually stopped working on it since the HTC SIP menu works.
Thanks for the info!