From these messages I cannot see what is missing, but the pear folder suggests a module for PHP. That is really easy in Wamp. Open the control panel and under PHP (might be php.ini) you can load addinional modules.
But as said, I do not know what module is missing.

Good luck

Warning: require_once(Auth/OpenID/CryptUtil.php) [function.require-once.html]: failed to open stream: No such file or directory in C:\Slamp\wamp\www\b2evolution\blogs\plugins\openid_plugin\php-openid\Auth\OpenID\BigMath.php on line 21

It would *appear* to be looking for the file in :
C:\Slamp\wamp\www\b2evolution\blogs\plugins\openid_plugin\php-openid\Auth\OpenID\Auth\OpenID\

¥

I tried on linux and I got this message
"The source for randomness (/dev/urandom) is not available. Please configure it."

[Edit: To avoid this error, add /dev/urandom to open_basedir in php.ini]

On an other linux host, I got openid plugin working but still not on windows.

Fatal error: require_once() [function.require.html]: Failed opening required 'Auth/OpenID/CryptUtil.php'

it's a strange error

Blueyed will know. Look for him on IRC