I've been working with a very interesting startup company specializing in nuclear medicine research and development. Since it is not possible to always be with the people you are working, it became apparent we needed a way to easily share documents and work in real time on a project. (If you click on the image you can watch it rotate)
I'm using dropbox to share documents. It's a light weight application which works on Macs and Windows and creates a shared folder. Anything in the folder is automatically replicated. Plus you can roll back to any version you wish. (bonus points - installing it on your own multiple machines makes sure you always have the correct file on hand). All you do is create a shared folder, put in the other person's email address, they click on the link - done.
To share my screen with anyone I love Adobe ConnectNow. It also works equally well with Macs and Windows. Because everything is done in flash, you don't get that pesky Citrix client install used by other companies. The screen refreshes are pretty good, but if you try to play a movie, there is too much lag. It's a polished interface where you can move a file, chat and even supports web cams. The only problem with that is I have to make sure I comb my hair before I start a session. You can be talking on the phone, fire it up and send them an email link from inside the application. They click and within a minute they are seeing your screen.
The price is right for both of these tools. They're both beta.
So make sure you have a couple of these types of useful applications so you can work more easily with your virtual teams without having to put in an IT request.