is there a big difference bwteen a 2700 and 3200 when it comes to gaming

depend on your Cpu

1gb is enough though

for most games 1 gig is great. you should have no problem playing the games with 1 gig aslong as your videocard and procecssor is good enough for your standards of play

Right now i have a 1gb or ddr 2700 and want to know is can i run games at its full potental or i should get a 1gb of 3200 instead. Some of the games i going to play are like doom 3 and nba live 2005 if you can answer than thanks. i have a 2.6mhz processor and a 128mb RADEON 9200.

First off, I'd try to get that cpu running at 2.6GigaHerz :p

For the games you've mentioned I'm pretty sure you'll get better performance from a new gpu, but they cost more than the ram... It'll allow you to use a better resolution and increase eye candy...

After that you'll probably be held back by the cpu (unless you're using an AMD64 and that is the actual speed and not the rating), and after you upgrade that you'll be held back by the ram... And then it'll be the graphics card again.... ;)

Since you don't tell us what kind of cpu you have, it's a bit hard to tell how much increase you'll get from the ram, but chances are you won't feel any change if you upgrade to 3200...

I have a 2 512 ram of ddr 2700 and a 256 ddr of 3200 and i wonder can i put all three in my motherboard (Also if i can't than which one should i use. i use my computer mostly for gaming)

If you have a FSB533 P4 2.6ghz

you are running at 133mhz that equal to pc2100 memory

so you have nothing to worry about your memory (as long as your not going to get a new system)

as MrGaribaldi has said

for today games, its time for a new video card

You should have added this to your first post, not start another one!
Never mix different speed RAM sticks (they would work only at the speed of the slowest stick, if you insist). They can cause all sorts of BSODs and other problems.
Keep the 2x512.