Well since you can get SHIII for $20 or less, I'd go ahead and play that and then you'll be ready to handle SH4 went it gets here next spring.
After you get SHIII, you'll need one patch, which is the last one. Just make sure to get the right version depending on how and where you got it.
I'd play the game in it's unmodded version for a while, then read up on information concerning various mods, especially the major supermods and decide for yourself what you'll like best, based on various threads and info around here.
Don't be afraid to ask questions. We were all noobs once.
