Help With Scanner E-Mail Button

My previous e-mail client was Eudora. When I used the e-mail button on
my scanner (HP Scanjet 4300 Cse), it would automatically open Eudora
in preparation for sending the scan via e-mail.
When I switched to Pegasus (quite a while ago), it stopped doing that.
Yes, I installed Pegasus Simple MAPI, but that didn't work.
When I open HP Button Manager, to set the button to use Pegasus, I
can't find Pegasus on the drop-down list.
Any ideas how to fix this?