No that isn't what I meant.
Taking my Pentium 4 as an example (this applies to your one as well), it has a 'quad pumped' Front Side Bus of 800MHz. The actual FSB speed is 200MHz (that's where the 'Quad' comes in). The speed of my memory should match that, unless I want faster memory for some reason (the common reason is overclocking). So in the case of my Pentium 4 I want DDR memory that runs at 200MHz, which is DDR400 (or PC3200, if you prefer).
As far as I'm aware, all Pentium 4 processors since the type one I have (Northwood C) use the same 800MHz FSB except for the 3.73GHz Extreme Edition, meaning that they also use 200MHz memory. The difference is that your motherboard uses DDR2 instead of DDR, so it's DDR2-400 (PC2-3200). (well, the CPUs are quite different but meh...in terms of memory).
PC2-4200 runs at 266MHz and PC2-5300 at 333MHz. So unless you have your processor's FSB overclocked to those speeds, your PC will be running your memory at 200MHz regardless of it's rated speed.
Buying faster memory is not really a bad thing. Were you to buy PC2-3200 now, you'd find that it's too slow for anything faster than a Pentium 4. But buying PC2-4200 or PC2-5300 gives you some leeway in the future
I'd get the 1gb of PC2-4200. I believe 266MHz is fast enough for every processor currently on the market, including the recent Core 2 Duo processors which are a big thing at the moment. And if it isn't fast enough by the time you upgrade your PC, well then you've got a decent spare PC with plenty of RAM.
RAM always comes down in price so I tend to think it's best to buy what you need now, and leave what you may need in the future...to the future. Because it'll be cheaper than it is now. I know I just contradicted myself because logically that would mean I'd tell you to buy PC2-3200, but as you have 1gb of PC2-4200 already it seems pointless deliberately buying slower RAM to go with it.
Also, mixing RAM brands is perfectly fine. 'Matched pairs' from manufacturers will be slightly faster, dual channel will work slightly better and they will overclock better. But unless you overclock (and if you did I wouldn't be explaining all this FSB stuff to you) the other two are so minimal that it doesn't matter.
wow thats alot to take in at once... haha. but thank you that did help alot... Now one thing I may have confused you on is this i am not running dual channel at the moment but i like too so would it help to get the same brand of ram that i have now allcomponets pc4200???? its a matter of $20 which ya seems so silly to even worry about but we are all trying to get the most for our money and yet the best performance as well. also in college at the moment so enough said. haha. I know i've asked this question already about brands but when you said the part about slightly better with dual channel i got worried. see when i first build thie computer i had tons and tons of issues from the get go. My cpu was getting about 80 c just running scan... NOT GOOD, so i sent it back to the place where i bought my barebones kit and they got back to me and said my mem was incompabile with my mobo. well i thought about it and i had 2g of $120 each sticks of ram or a new $100 board. Thats a no brainer. so needless to say i am now worried when i hear slightly better... maybe you can clear this up
As long as they're the same capacity and can both run at the same speed (which is 200MHz, so not a problem for PC2-4200) you should be able to run in dual channel. Matched pairs offer the best compatability, but a matched pair is something you buy as...a pair. It may be worth going for the extra $20, because it's not a massive amount extra over whatever you're paying already ($80-100?).