First things first: Does your MOBO support this ram in a 4x1GB config? There should be a ram diagram of what is the best supported ram configs for your mother board in the users manual.
You WILL lose Dual channel with three ram sticks Dual channel will only work with pairs. The newer intel chipsets have found a way to work around this but I believe you need to enable this in the bios... I could be mistaken. the best situation depends on if you play many games or do graphic design. Games, you should have fast ram in dual channel. Graphic design you just need ram, a lot of it, so the config 3x 1gig would work for you.
you might need to make some adjustments to your RAM timings *if your board allows it at least* As for what you need to adjust? There is no one set of magical numbers really. Its something you have to mess around with for yourself *or find someone else online who has done it and just use their timings* Something i have learned over time is that having dual channel with 4 sticks instead of 2 sticks tends to take a little more tinkering depending on what ram you have and your board.
The best place to start is to visit the forums of whoever makes your motherboard.
It would help if you gave us your system specs.
I kind of read about some issue like this over on the 1up boards while talking about crysis and thought I could bring it up here where people know what they are talking about heh...
Is it better to run 3x1GB or 2x1GB? Will I for sure lose Dual Channel if the Ram itself is Dual Channel by running the 3x1GB?
I have not heard anything about this...
Haven't read the 1up boards but I suspect they are talking about the unique brand of hell that is addressing 4G of RAM with a 32-bit OS. Not sure if it's directly applicable to your case but ...
Try removing the video card and seeing if your machine will then boot with 4G. This is idle speculation though, don't think there's a conflict here.
Try also using 2x1G and 2x512M RAM. I think this is your best option if it works (just sell off the extra 2 sticks of 1G). If you have a bad memory slot that's freaking out whenever you plug something in, well, I don't think that's likely either.
Or try upgrading to 64 bit OS. Make sure you have 64-bit drivers for everything. This is a bit more of a hassle but it's really the only way to go for 4G. (Or try stepping down to XP-SP1, before MS crippled the PAE. Your drivers might, uh, complain)
Going with the 2x1G + 2x512M lets you keep dual-channel and stays under (mostly, I hope) the addressing limitations of 32-bit XP
To answer your question, yes the video card memory shows up as system memory in the strictest sense of the word. A 32-bit OS can only allocate 4GB worth of memory addresses, but the way x86 systems are designed to run (back when computers only had like 64MB or ram) it was easier to allow the OS to allocate some of that addressing for your hardware because there was a lot of extra addresses. But when you have 2GB of physical memory, and your video card has 768MB, and windows is assigning the rest to your sound card, pci busses, etc... there are no addresses left over for your extra RAM to operate. This is why 32-bit XP usually does not "register" more than 3.2-3.5 GB of physical memory. Even the older boards usually support at least 4GB or memory for this reason.
As computers have become more powerful, the current generation of personal computers are the first to hit this hard memory address barrier, and yes the ONLY way around it is to get a 64-Bit CPU and OS, not just upgrade to vista. Luckily most modern processors and motherboards already support 64-bit addressing, but you'll have to do your homework on that one.
Even if the OS doesn't see all 4GB of RAM, it would be better (for gaming) to have all 4 sticks installed (instead of just 3) to enable dual-channel memory.
However, the OS is completely independent of the problem, as OP stated with 4 sticks installed the system doesn't post. (which leads me to think it's more of a hardware problem rather than a memory timing issue)
Two more things to try:
1) - in addition to trying each individual ram stick (as has already been done), make sure to try each individual memory slot on your mobo. It's possible one of the memory slots is bad.
2) - make sure to check your mobo manual to see what configuration of sticks and timings are supported. If memory timing ARE causing a problem, ensure your bios is set to AUTO for RAM timing and it should pick the memory timings that will work.
I know that this is an old thread, but for someone else that is reading, did you think about looking up what "one long beep" means in from your post? That could steer you in the right direction to figure out what the problem is.