My studio PC is running xp with the max of 4gb of ram. I use EWQLSO and Play has been a huge pain in the ass lately for me. Even if all other synths are frozen, a quick bounce to audio will many times have cuts in the sound.
However, there are always ways to work around it. I wouldn't recommend building an underpowered computer for what you want to do at all but you always have options. For example, I can run two or three instances of play perfectly so I would create a bunch of audio tracks for each instrument then bounce to audio, place it in the track, then change what's on play to the next instrument. Going back and forth like that is time consuming and adds a few extra steps which can hurt work flow but it allows me to work within my limitations. I just don't get too fancy with the various settings on play because i would have to reprogram them every time i recorded.
Upgrading soon!