Are you getting the above Event ID's in your System Event Log and your Small Business Server 2003 machine reboots? Well you'll be happy to know that you don't have a virus or a bug. But you'll be disappointed to know that more work is needed on your SBS machine.
After a certain number of days (not really a definitive answer on this) but if your SBS machine has not been promoted to a Domain Controller (by running dcpromo.exe) then SBS by design gives you these 3 events and reboots your computer every 100 minutes. It's a way for Microsoft to make sure that you use SBS the way it was designed and not for a regular Windows Server 2003 installation in workgroup mode.
A question popped up about this in a recent group posting and the user was concerned with the setup of SBS now that the client (or maybe more appropriately, himself :) ) had installed programs and data. Well really the SBS installation was not completed. SBS after installing Windows Server then continues on with the dcpromo exercise and then installs Exchange off of CD2 and then the other items as instructed through your installation choices including the installation of client apps such as Outlook 2003. So since Windows Server 2003 is installed and functioning to get around the reboot and event id's just simply reinsert CD1 of SBS and begin the installation again. Your programs and data won't be overwritten (unless you did something silly like install Exchange 2000 or something in the SBS media) and you should be able to continue on.
Now on the flip side....if you do this or are getting this then a big shame on you! Make sure to test your installs and any new media if you're unfamiliar with it. Even in small business environments we need to test, test and test again. And not just for a day or two but perhaps for several days or weeks, even 6-8 weeks out. A good example is SP1 for SBS. Have you installed it yet in production? Sorry not me yet. I'm just a little leary and I need more information on ISA 2004 for my premium customers and a longer period to wait out any issues that might be lurking out there. I don't think of it as delaying...just appropriate timeliness!