ZIAREHMAN :
yesterday i went to computer city here in Karachi.........there i asked about the q6600 in dell 745 they said me that there is no need to spend extra money on this PC you should go for dell precision 690 that this PC can fit any type of card and has a huge power supply he also said that this a server PC..........will this pc be good enough and this PC is also of same price as that of dell 745..... http://karachi.olx.com.pk/dell-precision-690-tower-highend-gaming-graphics-system-with-1000watts-psu-iid-511195075.....
OK. I read it again. So, do you actually have Optiplex or not?
If you do, it would be complete waste of money to get another used PC, which has to be upgraded. Actually, I just checked your link one more time and I see that this Precision is missing hard drive, so it is missing Windows as well, if it doesn't have Windows serial poste on the case, you will need to buy Windows as well - you will have to add at least about the same money as PC cost already. Also, it has professional, old Video card, which has to be changed anyway, because it is designed for different purpose, not for gaming, so I strongly advise you from getting this particular Precision.
Now question comes to your budget, you just were thinking about getting another old PC to upgrade and spend more money.
What is your real budget, since I helped others from Pakistan, I know your range of money, just state your amount budget, like for an example 20,000 or 40,000, don't convert to dollars.
I found plenty Pakistan used parts and PCs online, so I can see what is easiest and best for you to start, if you want to change your Optiplex, or upgrade.