I am familiar with creating a custom button to 'carry' a value over from object to object, but I am unsure if it is possible to fill a Picklist Field with a specific choice.
Here's the existing link, and I need to prefill Chance__c with the pickval 10% when creating a new custom object record from the Account view related list button.
https://na2.salesforce.com/setup/ui/recordtypeselect.jsp? ent=01I40000000IBaw&save_new_url=%2Fa01%2Fe%3FCF00N400000029JnV_lkid={!Account.Id} &CF00N400000029JoT={!Account.Additional_Owner__c} &CF00N400000029JoT_lkid={!Account.Additional_OwnerId__c}
https://na2.salesforce.com/setup/ui/recordtypeselect.jsp?
ent=01I40000000IBaw&save_new_url=%2Fa01%2Fe%3FCF00N400000029JnV_lkid={!Account.Id}
&CF00N400000029JoT={!Account.Additional_Owner__c}
&CF00N400000029JoT_lkid={!Account.Additional_OwnerId__c}