Which games on this rig?

your gfx is a little on the weak side but you will be able to play most if not all games out at the moment. you will struggle more with games like badcompany 2 and witcher 2 which will use as many cores as you have.
your unlikely to max out any games from the last year or so, but anything pre-dating crysis should max out at 1024/768 or 1280/1024
games like fear, dawn of war, starwars bayttlefront 2 should play well. games like masseffect will have to be run at either lower rez or lower quality. crysis you will be lucky to play at medium settings at limited rez.
oh and forget turning on dx10.1 specific attributes in games it will just crush your gfx. play em all in dx9 mode for the smoothest experiance.

http://www.youtube.com/watch?v=jVXRZ6wJal0 look at this vid for AC for instance. everything at medium or there abouts and it still looks quite good and the framerate although is struggling to keep 30fps is smooth enough to be playable.
there is noticable problems in the drawdistance in that the shadows seem to be limited to 20-30 yards in front of you, but it is suprising how good this little card is when you think about it.

over all its not what i would class as a gaming card as its best run at 10/7 for most games and will struggle to get past medium settings on anything new. its very much entry level, but if you accept that its very limited you will enjoy the games it can play. but honestly it is a hd video card rather than a gaming card and it will play hd video very proficently...

Any idea abt Black Ops's perfomance?

it will run on low settings for multiplayer and a little higher on single player.

will there be a lot of difference if i upgrade the Dual-core 3.0Ghz to a Corei3 2.93Ghz? or should i invest that money on a better VGA card?

No, there won't be a noticeable difference if you upgrade from a E5700 to a 530. Invest on a better GFX card or GPU.
1)What's your PSU ?
2)What OS are you using ? Also it's memory interface ( whether it's a 32 bit or 64 bit )
Buy more RAM as well.

e5700 is an ok cpu. but really its time you jumped on the quad core waggon even if you just get a q8300 or 8400 it will be a worthy upgrade.
gfx wise the ati 4850 or 4870 and 98gt would be the best peformers with your current cpu config. if you go higher you will just bottleneck your games and get less performance than expected.

1. 315W PSU
2. WIN 7 ultimate 32bit

Thought of upgrading to a HD5450. or is HD4350 better than it?

Could you state your budget ?
HD 4350 to a HD 5450 ? Not much of a worthy upgrade.
What's the brand name and the model of that PSU ?

What you should do is, get a better PSU and then a good GPU. For that CPU, I'd say a GTS 450 or HD 5770 would be okay, considering your budget as well for BOTH PSU and GPU.

PSU is a good one & it is real 315W.. well i wish i can get the 5770 or GTS450, but im not that rich   so guess ill go for the 5450, also my monitor is a 22inch CRT, so 512MB wont be enough i guess.. should go for the 1GB isnt it?

Real 315 W PSU ? Haven't heard of it. Could you please be a bit more specific.
I ask my question again.
1) What is your budget ?
2) You may want to add some more RAM as well. Since you have a 32 bit OS, you'd be able to use about 3 or 3.25 gigs. Any chance you can get a 64X bit OS ?

COD4 on your current system would run maybe at 1024X768 with lowered details. And Crysis ? Not sure, but you'd get to run it at 800X600 all on low, and maybe a few settings on medium.