just wondering if anyone has any ideas for creating the folowing?
different posses for dragon knight and war priest?
dragon gaurd(elite asterlings with halberds)?

Unless you pick up alternate models from non GW locations there really is little for options in LotR. The LotR line is a 25mm range, instead of the 28mm heroic that fantasy and 40k are. I guess you may be able to use Chinese or Japanese ancients, but the armor wont be exact. If you are good with greenstuff though you could make them work.

Most of my conversions have been brass rod for pikes and the standard stuff like head and hand swaps to change looks a little bit.

do you think the perry minatures samurais would work?

I believe so. I think the are 25mm standard, so they should be comparable in stance and design. I would recommend getting a couple models to use as a comparison with the official models. Just remember that using Perry minis will preclude you from attending any official gw events.