Don't know if u've solved the problem yet, but i had a similar issue with .001 .002, etc files...

Try dowloading a utility called HJSplit, here's the link http://www.freebyte.com/hjsplit/#win32

It pieces together all the files to make one whole archive, can also split too as the name suggests. If that doesn't do it ur surely stuffed !!

I just ran into this problem the file naming scheme started with .001 down to .020 and i kept trying to unzip or use poweriso. It was indeed Hjsplit. A free program used to split and join files. i didn't look at how old this thread is but, i'd say im quite computer savy and usually have no problems recognizing a compressed split file. this thing is only split it seems.