I think 2GB is nearly the upper limit if u decided to stick to 32bit OS, because if u using 4 GB, windows will only display up to 3.5 GB, it will become even lesser than that if ur GC has lot of memory to be addressed, so its kinda waste

if u install 3 GB, then it wont have dual channel, which...erm... doesnt matter so much actually

now still isnt a mature time for 64bit computing, if the windows vienna thingy comes true in 2010s, then that will be the flagship OS which will focus entirely on 64bit

a 4GB will never enough for 64 bit systems, expect future RAM DIMMs will come in 4GB or 8 GB per stick