draggono it seems you've been given a lot of conflicting and confusing responses here. I'll try to answer your questions for you.
Your 32 bit OS is limited to addressing 4GB RAM. If you install 4GB you won't be able to access all of it directly since the OS needs some of the address space for various overhead such as graphics card memory. 4GB will still be better than 2GB but how much depends a lot on which OS you're using. Vista will take advantage of the extra memory much better than XP will. You will probably see anywhere from 3.3GB to 3.6GB of available memory in Windows which is pretty close to the full 4GB and a lot more than 2GB. Windows limits it's applications in a 32bit environment to 2GB each but that still means that they'll be able to use a full 2GB (if they need it) without having to utilize the page file because there'll be plenty of extra memory for the OS and other things.
Vista is very good at using available memory and will run noticeably smoother and faster on a 4GB machine over a 2GB machine and will actually claim approximately 20-40% more memory for itself(I know this personally from direct testing).
XP will still use the same memory and won't run any more efficiently or smoother on a 4GB machine until you open enough applications to push that 2GB limit so it depends on what apps you use.
So if you use XP and never push more than 2GB total memory usage don't bother. If you use Vista go for it and get the 4GB! Vista really shines on a 4GB system.
As far as the RAMDisk idea....don't bother....here's why....With 4GB memory Windows probably won't every actually need the swap file and won't use it. If you make a RAMDisk for your swap file Windows will use it because it will be short on memory....it's kind of self defeating so there's no point. Besides, your swap file should be at least as large as your total system memory so it's not a good idea to use a 1GB fixed swap file with 3GB left over for Windows....best just to let Windows manage it. In an ideal environment you should put your swap file on a separate physical drive (not partition) but in a notebook you usually only have one drive and like I said before, with a 4GB system Windows will rarely use the swap file. Besides, I'm not even sure your idea would work to give you the full 4GB but IMO it's not worth trying.
About dual channel. I'm not sure why your notebook says it doesn't support dual channel so maybe because it's only got one stick installed now....not sure about that one but it could just be that particular motherboard doesn't support it. Like the others said, it's not a big deal and dual channel support offers negligible performance advantages with current Intel based systems anyway. Dual channel support is a bigger deal on older AMD based XP and A64 systems. With that in mind, 3GB would work well for you as well if you don't want to get the 4GB (resulting in 3.3 to 3.6GB of available system memory).
To find out what RAM you have installed now download this nice little application called CPU-Z from here:http://www.cpuid.com/cpuz.php
Just run the app from within the folder (no installation required) and look under the "Memory" tab for what you memory is running at and under the "SPD" tab for complete information about your installed memory's supported speeds and latency.