Hmm I had a good deal of success running GTAIV on the following setup at Medium:

Intel Core 2 Duo 2.53 Ghz (sorry don't remember the exact numbers here)
8 GB RAM
512MB Nvidia 9600GT

I'm inclined to believe that either your CPU or memory is the major issue there because I was able to play a smooth 30-40 FPS (which, given that its GTAIV is pretty good).

I would definitely at least upgrade to 4 GB of RAM though, Windows 7 has a huge memory footprint.

as others have said gtaiv is very poorly optimized, but you still need at least a 2 gig more of ram, a better graphics card and if you can a quad core processor(or 6 if you got money) and you should be able to run it ok.

Not quite, I have never had trouble running it even with a 4850 512MB. The key with GTA IV is it's a processor intensive game. Even someone with a GTX580 can have difficulty running it while overclocking your CPU will yield significant framerate increases.

could be right Delixe, ran like crap on my old dual core machine before i upgraded to a AMD PHENOMII BLK X6 1100T 3.3GHZ 9MB AM3.(also help that i upgraded graphics as well)

back when the game came out I upgraded from a dual to a quad core cpu. That changed it from sluggish to (somewhat) smooth. I was running a 4870 at that time.

I probably should.

Have you tried lowering the resolution?

Yup.
I've basically lowered everything to low/medium and the resolution to 1280 x 720 and it still hiccups from time to time.

I played that game with 9800gt.. Worked fine, pretty much. Now I have ati 6850 oc. Same other things. I got the feeling that the newest patch made even original gtaIV to run slower.
Good game but it really is poorly optimized. It runs.. but It really is suprisingly crappily made for pc.
And I bought that bundle mostly because of episodes. Haven't played those bastards.

I've got a 3.6Ghz OC'd i5 quadcore. I can't max out view distance without dropping below 50 FPS.

Bad port is bad.

30-40 fps is the best you are ever going to get out of it. It's perfectly playable. You can say bad port is bad but in truth bad engine is bad. It ran like crap on consoles as well with the 360 version falling below 25fps at night time.

If it looks as dated as GTAIV does and I can't get a consistent 60FPS out of it, then it's a bad port.

On a dual-core anyway.

Did some more experimenting with the graphic options, i managed to max almost everything to high by lower Textures to Low and i'm running the game at 1680 x 1050 at playable FPS.
No idea why FPS take such a dip between Low and Medium <_<