The password is for the PKCS12 file itself, not for the private key. You can specify an empty password by adding "passpass pass:" as follows:
$ openssl pkcs12 -password pass: -export -in myprivatecert.pem -nokeys -out mycert.p12
Windows will still be prompted for the password, but you can leave it blank and the import will work fine.
, Windows, , , DER :
$ openssl x509 -in myprivatecert.pem -outform DER -out mycert.der
, Windows der . , .