Ok, here's the trick, I've been cracking AD password for donno how many companies I've worked for here's the rule of thumb:
1) You need administrator priviledges, make sure you got that in hand.
2) use fgdump.exe on the local system (it will save it to a text.file), ensure that any anti-virus is disabled first (trend micro will zapped it before you'll able to copy it to c: drive of the server).
3) if the AD password hashes contains a list of users with their histories enabled, you need to use Excel to remove all those users with their histories before you start to crack (so use Find->Replace-> *.history* to remove the redundant histories password hashes.
4) search for torrent for the Rainbow crack files, the one I have for alphanumeric (which is good enough), however the full table is around 34gb which is huge! -> http://rainbowtables.shmoo.com/
5) load up either John the Ripper , or google for the now defunct symantec lophtcrack 5.0, I think the *.exe file is still around somewhere. (however, do note that John the ripper cannot differenciate between upper and lowercase).
6) crack the file with the rainbow tables which should take you less than 15-30mins depends how many AD users are there in the AD.
Hope that helps.
Done all 3 certs, now going for CISSP.....