WELCOME ABOARD!
I currently have a five-year-old Pentium 4, which I have upgraded to 4GB RAM and a 1GB ATI 4650 video card, and it runs SH4 maxed out. That said, I'm looking to upgrade soon because it won't run SH4, and, believe it or not, it has trouble with SH3 (mainly due to all the mods I have installed).
Try to talk to UnderseaLCPL. He has a Mac, and I think he runs these games on it.