Driver install can't find avcstrm on XP SP2

I'm writing an AV/C Subunit driver I'm trying to install on Windows XP
SP2. I'm trying to get avcstrm.sys to load under it as a lower filter.
It fails and setupapi.log indicates that avcstrm.sys cannot be found.
I looked around and the only place I could find it is in
"%windir%\Driver Cache\I386\SP2.CAB".

What's the recommended way to get it out of there and into
%windir%\system32\drivers where the system can find it? Normally I
would expect it to be located through an AVCSTRM.INF file, but there is
no such file on the XP SP2 system.

I looked at the docs for the [SourceDiskNames] section in an INF file,
and it says the 'path' component of a "diskid = ..." statement is
relative to the installation root. SP2.CAB will not be on my
distribution media at all, so I do not think that is applicable, but I
have to specify avcstrm.sys somewhere in a CopyFiles section somewhere,
right?

For now I have manually extracted avcstrm.sys from SP2.CAB and put it in
the system drivers directory, but if someone could tell me the proper
way to accomplish this I would be grateful.