Is there any way to sign in yahoo messenger usuing 2 yahoo id's?

Yea! I know what you're talkin about. Go to yahoo mail-> then go to options and then hit "add" make a new id and then when you log in you have 2 ids loggin in at the same time. and whnever you wanna talk to a person, there is a option on yahoo messege IM's , hit there you'll find you're new ID!

Yes, you can make 2 or more usernames on YIM on the same account

You would only be able to do this using 2 computers