I've got the same problem on my Macbook Pro, and I found a solution. Not sure it will work for you, but it's better then nothing.
1. My macbook pro lets me install windows 7 only if it's burned on DVD+R(or RW) disk. DVD-R(RW) cannot be detected by my bootcamp assistant since I upgraded to 10.8, I don't know why.
2. Bootcamp recognizes ony FULL RETAIL copy of Windows. First time i tried to install a costumly modified version of Windows 7 - it did't work, then a Full Retail copy on DVD-R, - no luck again.
And finally, when i tried a Full Retail copy of Windows7 burnt on DVD+R, - bootcamp recognized it and all further installations were going correctly, no problem at all.
Try to use DVD+R(RW) and some different Windows 7 editions, if you have them.
Hope, this could help you.
P.S. Sorry for my weird English))