Now I'm lost completely.
As I mentioned before my servers mount XP shares - this is not true:
I have few AIX 6100-02-04 - they mount my XP machine share with no problem.
Have one AIX...
You need to install bos.cifs_fs package.
Keep in mind that if you want to mount Windows7/Server2008 share, packages I mentioned should be >=TL4(AIX 6.1).