When windows was still on my disk i had the same problem.
Now... first: free does support them and it's easy to mount the logical
drives in the extended partition with freebsd.
With netbsd....:
Its also possible but not that simple, when you have netbsd on one disk
and windows on the other you can call mbrlabel over the disk with the
logical partitions. After that run disklabel over that disk and you'll see
what you can mount. It worked fine with me then, that was
version 1.4 for x86. I must add that you must be carefull, do NOT run
mbrlabel on the disk on which the netbsd partitions are mounted, cause 
mbrlabel will replace the disklabel's with virtual ones.
So this is gonna work if you got netbsd on one disk and windows on the
other. I guess it still works for 1.4.2, i only did it with 1.4, didnt try
it on 1.4.1 and 1.4.2
I guess this is what Frank meant with the patch.
Bye,

Reinoud.