Ram is needed more in bigger areas. Larger maps, lots of people, lots of things moving. etc. I would even suggest another 1GB of ram to be on the safe side. As for processor, as long as its not old like P4 2.0ghz and under, old stuff like that, then you should be fine.
Patches, I think you can just download the latest one and it just goes from there. I haven't played BF2 in a while, so I can't recall or know any changes on how to do it.