XFX ATI Radeon 4670 on Dell Gx620?

Yes you have already guessed it. Will the ATI Radeon work on my Mid-Tower Dell GX620?

My system specs are as follows.

Pentium 4 3.0GhZ with HT,
512MB DDRII x2,
80GB HDD @7200rpm SATA,
LiteON Combo.
PCI-e x16 slot.

It has a 305Watt PSU. I know its a limiting factor, but I have seen people running the ATI Radeon on it, though I'm not sure if it will run on my system considering the specs of my system.

I'm running my system on 1024x768. So will the card work on my system? considering I'm not a serious gamer (just play fifa10 and NFS Shift sometimes i.e., nothing close to extreme gaming).

Presuming if it does manage to run, will it affect the performance level?
I'm changing my 80Gb HDD to 250Gb HDD, will it affect the total watt usage to HDD?

Thanx

{P.S. im a noob  }