HD:System:Library:PrivateFrameworks:MediaKit.framework:Versions:A:Resources:MKDr ivers.bundle:Contents:Resources: bootroot.loader

Could you tell me if this file exists on your (Intel) Mac?

On our PPCs running 10.4.8 there is a similar file with the
same path, but named 'boot.loader' rather than
'bootroot.loader'. From poking around, it looks like it's
part of a boot procedure. That's not to say that the one you have is right or wrong for an Intel Mac. But it might have
the different name on an Intel Mac so that it could co-exist
with a PPC bootstrap loader in the same folder.

Can you tell me: Is this a zip-bomb - or not?

Well, you could submit it to the virustotal.com site, where
it can be scanned (for free) by all of the various virus
scanners, and you could compare the results. The link is
here:
http://www.virustotal.com/en/indexf.html
Click the 'Browse' button at the top, navigate to the file, then click the 'Send' button. To make it easier, I'd option drag (to make a copy, not move) this file to your Desktop, then browse to it from there while on the virustotal.com web
site.
That's a handy web site if you have PCs - they always have viruses.
Hope this helps,
Russ
Xserve G5 2.0 GHz 2 GB RAM Mac OS X (10.4.8) Apple Hardware RAID, ATTO UL4D, Exabyte VXA-2 1x10 1u