I guess the answer is ..... it depends ..... on what you want to do.
Writing this on a Dell similar to the one you spec'd out, I'm listening to music running on a MacBook Pro with 4 Gb RAM (tho' a MacMini would work as well but I no longer own a TV or standalone monitor). Having gone through learning several OS (CPM, MS-DOS, OS/2, Windows 3.0/3.1/95/98/XP/Vista/Win7, and assorted Mac OS) I think it's really just a matter of learning enough of the OS for your application. While using WIN7 for work/general use, I find the Mac Snow Leopard easy to use and not so different than Windows.
What it came down to was software. I had the chance to try Pure Vinyl/Pure Music which works well and SOUNDS good. Once I'd decided on Pure Music I was tied to a Mac.
So, if you can justify a separate computer JUST for music, you might consider a Mac since learning enough of the OS to work with it is pretty similar to Windows and you can easily run a good player such as Pure Music and (as I have) use an iPod Touch as a remote.
btw I use a mirrored pair of 1.5 Tb external hard drives to store my music in WAV and Apple Lossless
