hi i was a similar upgrade situation like you a few months earlier
i had an athlon 64 3000+ and i decided to go with the x2 4400+. i can vouch that it was worth all the money. it's really noticably faster and you will feel the difference among all programs that you're using. plus, i overclocked it easily from stock 2.2ghz to 2.4ghz which makes it essentially a 4800 now. isn't that a bargain?
i understand the situation because i dont' have money to get a new intel system right now either. in my opinion, right NOW is the last chance for us socket 939 people to get an upgrade, because after this AM2 will take over and we will basically become computer junk.
however, the 4400+ will still keep our computer competitive (it doesn't tag that much behind the core 2 duo e6600 in most benchmarks), plus with your pretty good vid card and ram, it will last that much longer.
so hopefully that has helped you some