I'm not sure where, but it's got to be in the eXpress database since the console displays it on the properties page of each machine. You could do a SQL query against your DS to report on who has it & who doesn't.

Also, you can see the status in the registry at HKEY_LOCAL_MACHINE\SOFTWARE\Altiris\BootWorks Install\Status

[blank] = not installed
"Complete" = installed
"Bootworks installed successfully" = installed
"Error: ..." = problem with bootworks

I use a CustInv to get this value into the NS for reporting.

Hope that helps.