A while back I posted on EN World to get the differences/similarities between these 2 games. Since this time I have mastered the 2e WFRP rules and now would also love to be able to GM Dark Heresy. Some of the answers I received to this question at EN World included:

"WH40K is the same ruleset as WHFRP2, but slightly more complex in play due to guns, automatic fire, cover, pinning, etc. But overall the two systems play very similarly. If you know one, you know about 90% of the other system."

"The rule sets for both the games is very similar, but there are some differences. The career system as stated above is different, in wfrp you advance from one career to another unlike dark heresy's single career path. The stat block is a bit different too, there is no perception characteristic in wfrp, and in wfrp there is an additional group of secondary characteristics. Besides that the differences are minor. Though i do think dark heresy is more complicated, but not by much."

"You can dodge ranged attacks in Dark Heresy."

"Damage works a tad different in Dark Heresy as opposed to how it is handled in WFRP. For example: Let's say you have 3 wounds left, and then get hit in the arm for 5 wounds after armor and such.

In WFRP, you would be at 0 Wounds, and roll a d100 on the critical table with a Critical Value of 2 (for going 2 over your Wounds). This would give a Critical Effect of 2 to 7, which you would then look up on the Arm critical table. This would lead to a variety of results, ranging from just being unable to use your arm for a round, to turning your hand into a bloody mess that might never be usable again and having a 20% chance of dying from blood loss each round.

In Dark Heresy, you'd just look up the "-2" result on the arm critical damage table, which probably isn't all that bad (I don't have the table here to check).

Now, let's say you get a second hit for 3 points of post-armor damage. In WFRP, you never go below 0 Wounds, so you'd treat that as a new injury, rolling with a critical value of 3 (for 3 points left after your Wounds are gone). In Dark Heresy, however, you'd keep going lower, so you would check the critical tables for a value of -5."

Are there any other differences I should know about?