Should I upgrade?

I currently have a pentium 4 2.4GHZ with 1gb memory and a GeForce 3 Ti 300 video card.
Will it make a big difference if I get a Geforce 7600GT, 3.2GHZ Pentium4 and another gb memory when it comes to gaming? Also, what PC game has the highest system requirements?
I was also thinking about getting a new mb and a pentium D805 overclock it a bit and see if that will be good since upgrading will be around the same as getting all the new stuff.