1) IDE hard disk drives are slow. If you have one and want to use it, it is your wish.
2) You need DDR3 RAM for this. I don't know whether you have DDR3 RAM since you said you are replacing a Pentium 4 machine.
3) "peripherals are fairly new i just have to buy a mb and cpu" - how would we know that the components/peripherals you are talking about are "fairly new"? Mention those. This forum is all about being specific on what you have.
4) Revision 3.1 of Gigabyte 880GM-USB3 has a black AM3+ socket. If you get one you'd be able to fit in the next generation of AMD processors which came out last quarter and might come out this year. So, get the AM3+ revision 3.1 of the motherboard.
5) "few years" - hard to guess. most likely Intel and AMD are changing their sockets next year. CPU technology keeps on evolving and it gets harder to maintain compatibility. "Few years" is a lot of time.
6) "flash games" - okay will run fine. "Steam games on good settings" - which Steam games? What settings? Running games depends on the GPU, not CPU.
7) Power supply - I doubt you have a good power supply. Read this thread -
*www.thinkdigit.com/forum/power-sup...89-power-supply-blacklist-thread-newbies.html You'll have to change your Power supply too.
8) Processor could be Athlon II X4 640/45 or Phenom II X4 840. Both cost around Rs. 5000.
Time is wasted in asking these questions, and that's the reason why we tell everyone to fill up the questionnaire and answer every question asked their in accurate manner.