i know its old lol thats why i am planning to upgrade my graphic card now.
but the problem is, i am a student with limited income from part time jobs so i want to save as much as possible..
currently the pc has 500 watts PSU ( not sure which model ) and i am planning to get the HD 7870.
i have heard that 7870 is not a power huger card ( compare to like gtx 570 )
do u guys think i need to get a new PSU???
Yes you're right about 7870 being very efficient, it's a very efficient card. You at least need probably about 34A (Minimum about 28A) on the +12V rail with two 6-pin PCI-E connector on your PSU. If you do have that on your PSU, you're very safe. If your PSU does not meet the limitation, I think you should buy some better PSU .
Whats the specs on your rig? 7870 maybe overkill and you could possibly pick a different card that is more efficient for your PSU if that is important. The 6850 only needs one connector for example and is a very good card as well.
I bought a Asus DCUII 7870 and it calls for a minimum of a 450w PSU with a 12v current rating of 40a. Although if you do lack the PCI-E connectors and its of low quality it would be a good idea to upgrade that anyway.. You'll be happy and see some very nice gains from the 7870 over your current one.