DHCP options utilizing classes, or not

We have a few netboot machines around that require dhcp parameters
that differ from the standard for the rest of the machines.

Currently we utilize isc-dhcp for this purpose, but as we are moving to
AD we may need to use msdhcp.

for example, dns servers:
windows: 192.168.2.21
netboot: 192.168.2.22

I attempted to use vendor classes and created a new vendor class
which identified the netboot client via the vendor information, pretty
straight forward. created a new entry for dns servers and assigned it
to the class.

Using a packaet analyzer, the value for DNS servers was still for the
windows
servers, but on closer analysis it had crammed the option number, number of
bytes
and ip address into option 43 (trying to track down whether or not that is
what
is in the rfc). Which is a pain because it does not have the desired
effect.

User classes will not work either as the boot agent does not send out any
user
class identifier.

Is there a way to accomplish what I want?

Adam