i am thinking about getting a 5770 to replace my 7800gtx so i can play arma 2. Does anyone know how the card holds up in arma 2 or other demanding games?(couldn't find any vids of it in action on arma 2). Also, im not sure how bad my crappy cpu(intel e2180@2.4ghz) will hinder its performance. 
 
full rig atm:
  
win xp 32-bit
3gb ram
e2180@2.4ghz
nvidia 7800gtx
 
thanks

Your processor is definitely going to hinder its performance, sorry to say. 
 
The 5770 is a solid card and very good value for money, but it's not going to play Arma 2. That's not a huge downside though, since no card can play Arma 2 at the moment. Even the GTX 480 gets less than 30fps. It's less optimized than Crysis and by far the most demanding game at the moment. 
 

I have two in my computer.  They're very good cards and they run extremely cool. When Crossfired they run at about the power of a 5870 but even a single card will get the job done.
 
One can handle most games you throw at it.  You won't be able to max Crysis but you can run it smoothly on high settings with 4x anti-aliasing.
 
And yes, that processor will hinder your performance.

oh and btw i will be running games at 1680 x 1050 not 1080p
 
full rig atm:
  
win xp 32-bit
3gb ram
e2180@2.4ghz
nvidia 7800gtx

i say bite the bullet and just save up for a whole new rig, it will pay off in the long run.

Even if you cpu bottlenecks the card, it's still a way better card than your 7800GTX which would be absolutely unacceptable now for pc gaming. The hd5770 is slightly below the power of a gtx260, still it's acceptable. You might not be able to get all the framerates out of it, however you will notice an improvement.

Runs super cool and plays most games on high settings at 1080p. However, the 4770 is $50 cheaper and apparently benchmarks as well or better than the 5770, but doesn't support DX11.
 
I'd recommend it. Or maybe go for a slightly higher end card. Depends on what you want to play.
 
Oh and make sure you have PCI-e slots on your motherboard. Old motherboards may not be compatible with newer graphics cards, so watch out for that.

4770 does not compare to the 5770

Ive heard nothing but great things about it and im planning to get one for my next upgrade.

I'm sorry, I must have been thinking of the 4870.

jmrwacko is right, you're best off trying to get one of the higher end HD4000 series cards. They're probably really cheap now and you'll get better performance for less money.