Well, when windows first starts, it will, in most cases, be sending out DHCP discovers, as well as all the browser info (no, not a web browser). Hrm, windows may also be checking for updates (but I doubt it since you're running 98) and it could be trying to connect to mapped drives. There are more things it might be trying to do too.
Ya know what? Windows does all kinds of stuff on boot. I seriously doubt you have anything to worry about. If you are that worried, then get a good anti-virus program and check yourself out. I'm willing to bet that there is nothign there though, at least related to this.