Get user id from membership

Hi,
I am using Oracle tables (ora_aspnet_users, ora_aspnet_roles, ...) in my application. I add a user using:
MembershipUser mu = Membership.CreateUser(...);
I then try to get the user id using:
mu.ProviderUserKey.ToString()
It returns something like "463edddc-914b-..." whereas userid in Ora tables is defined as raw (it would be something like 1483E504BAF5..., no dashes).
What am I missing? When I try to insert this value into a table, using a parameter defined as "OracleDBType.Raw" it throws data binding error.
Thanks.
...