I haven't used personal Oracle 9i, but I use personal Oracle 8i a lot, and have used it for quite a while. I would assume the constraints are the same between 8i and 9i.
You have to separate what you CAN do from what you are licensed to do - they are different.
Personal Oracle is not intended to be used as a server. It is intended for all connections to be local. You can connect as many times as you want, but they are supposed to be local connections. One exception is that you are allowed to connect remotely for database administration. You will notice that with a Personal Oracle database you do not have an entry for LICENSE_MAX_SESSIONS or LICENSE_MAX_USERS in your parameter file because there are no limits. You can legally have as many accounts and as many local sessions as you want.
That being said, it is possible to connect to Personal Oracle remotely just like with any server edition of Oracle. However you are violating you license agreement if you do this for any reason other than administration.
