As by the title of your thread, any Pentium Dual Core has a much more efficient architecture than a Pentium 4 era processor and, generally speaking, will be quite a bit faster.
As to your post, no you can not run GTA4 without upgrading.
At the very minimum you will need to upgrade your GPU to a 4650, with a faster GPU being highly recommended.
If you are running Xp, GTA4 should still start with 1GB RAM, Vista and Windows 7 require a minimum of 1.5GB.
Personally, I would upgrade to 4GB regardless.