Yep, you can do it. Here's instructions from Yahoo:
"Additionally, while we strongly suggest that each manager participating in a live draft uses his/her own computer, it is possible to have multiple managers drafting on the same computer.
In order for multiple managers to draft at the same time, the first user would log in, open the Java Draft applet, and then log out of Yahoo while keeping the draft window running. The second user (and any subsequent users) would then have to log in and launch another draft client. "