Lots of early 64bit adoptors found/find themselves in your shoes, it is getting better and will be even more so when vista is released as this will push developers to release 64 compat drivers.
Take a look at avast 4.5 click here as you can see from the feature list, it is 64 bit compat. Not sure if this is a free version or not.
google page for 64x firewalls, suggest you google for any other drivers/patches you need, may be out there, may not.
Hope this helps.