Teams grow and change. New members arrive and they need to be accustomed to the culture of the organization, the project and the process.
This might be a frustrating experience both for the newcomer and for the team. Virtual environment makes it even worse. Lunch breaks with the colleagues to ease the process are not possible and there is no watercooler for chitchat.
In an office environment, it's a common practice to have a couple of meetings in order to introduce the new person to the project she's supposed to work or into the organization. But in a virtual environment, it's a bit harder to put the focus on meetings. Web conferences can be done, but they basically help only with the introduction, not with the integration.
In my opinion, a virtual organization should accomplish at least the following prerequisites in order to make the new one productive as soon as possible.
Make the newcomer feel part of the team
That's easier with a physical presence: an actual office, going out for lunch with colleagues, t-shirts with the logo etc. In an online environment, if the organization has a blog make an author account for the new guy and encourage she/him to write a post to describe his feelings regarding the new environment.
Assign a meaningful role for the newcomer
She or he might feel overwhelmed with the information needed to be absorbed.
The tricky part is that you cannot afford to have one of the team members absorbing all the information the other members have. In theory, it's a never ending process: by the time she would have the knowledge an existing member had, that one would be far ahead. And after all, the knowledge one team member has shouldn't completely overlap with another. Everyone should bring something new.
The solution is to encourage the new one to dive into work and try to complete an easy task. The task should be a real one, because otherwise the motivation to do it will be diminished. This way you also bring out the practical aspects of the guy, which is probably why you wanted him in the team in the first place.
Have all the tools configured for the new account
Don't let the guy wait around a couple of days or weeks because he doesn't have access to the tools you're using with the others. The new account must be easily created with the appropriate rights for the newcomer in every application you're using: blog, wiki, tasks tool etc.
Document your decisions and procedures
This is an ongoing process, from which everyone in the team benefit, but it will prove itself useful for a new member as well.
There would still be a lot of questions and interruptions for you and your team to help the new one get acquainted, but a lot less than without a proper documentation. And the documentation shouldn't be built just before a new one comes, but throughout the life of the project/organization.
This is so easy and straightforward to do, but still disregarded by many: write everything down. If you need to explain a procedure or a feature to one of the colleagues, after you discuss on it go and write it down. Don't use applications designed for something else, like Word or Visio or other UML or word processor, but some simple text wiki/message environment, which allows for easy editing afterward and it's easy to share.
Procedures usually change in time, so the more difficult you make it to update them, by drawing schemas and format text, the less likely that you'll do it, rendering them obsolete.
Provide feedback often
Don't keep the newcomer in suspense. Let him know often where to pay attention, what to improve in the process and ask him questions. Leaving the guy one week to read documentation is boring and will make him loose focus.
Keep an up-to-date list with the existing members and their roles
The new guy will have questions. A lot of them. Don't allow for his questions to bounce around from one guy to another, until he finds the proper person to ask. Maintaining a web page with who's in the team and what everyone is working on might be a time saver.