Ok so i was talking to my friend and i told him i was going to change my gpu for a ati 5770 and he told me that with my cpu (intel core 2 duo E7300) there was going to be a mayor bottleneck. Can anyone confirm this, thank you.
games like battlefield series, s.t.a.l.k.e.r series, half life, bioshock, etc. My resolution would be 1280x960
That "etc" may eat your day alive. Otherwise, its not a problem at all. What frequency do your CPU run at? These games you've mentioned LOVE CPU frequency more than core numbers. And your 5770 will be a bottleneck before E7300 is, and its especially true if your OC your E7300 to sub 4 GHz level. But things will not be as dramatic when you choose to play something very demanding. At that res, do you actually NEED 5770 to play those games? I mean... save some money and buy a 24" monitor first, then you could get a higher end card. Otherwise, your hardware will be starving....
For Stalker,HL and Bioshock it should run fine without a problem.
As for BF series,well BC2 benefits from a faster CPU, and since lower resolutions benefit from CPU too,then your card may not run at its full potential,BUT it can handle the game fine without problems.
Your bottleneck is always your hard drive unless you have an SSD.
The OP seems to specifically be asking about games, so the HDD would really only bottleneck loading times. Not the prime subject of concern if confronted with a budget.
That aside, as already mentioned, resolution plays a huge factor here. At only 1280*960 there shouldn't be too many issues with a HD 5770 bottlenecking your games. Use a higher resolution and the story changes.