Unbuffered RAM is what is used in normal computers, buffered is used in servers.
the proper term for "buffered" RAM is ECC. ECC memory is of course used in servers and for other applications where data integrity is of the utmost importance. The downside is that ECC RAM will be about 30% slower than non-ECC RAM.
Putting more RAM in than the motherboard's limit will cause the motherboard to fail to post...
Not necessarily. Sometimes it just won't recognize the memory beyond it's limit. It depends on the motherboard design, though.
The Aspite x1900 according to the information I found maxes out at 8GB of Memory. Crucial
sells kits for that particular upgrade.
Or anybody heard of being able to successfully use more RAM than the recommended specs?
No. They aren't "recommended specs" they are a inherent limitation of the design of the motherboard.
Or anybody heard of a program that allows you to utilize more RAM than the normal specs?
Yes. Early on (say mid 80's) you could upgrade the 1MB of a IBM PC to higher amounts of memory by installing Expanded memory, which was managed by an EMS driver and programs aware of Expanded memory could access it. However, today, No. No such programs exist.
More to the point, however- no such programs are necessary, because the way all modern operating systems work involves using a page file and "virtual" memory, which oversimplified basically means that when the computer needs to use more RAM and there isn't any physical memory available it swaps some used physical memory to the swap file and uses the now free memory.