my biggest mistake??
hmm..
tough one..  well, I never really made a BIG mistake (yet), becuase I follow the industry about a year after everyone else (so I can see what's good and what isn't after the dust settles).
the biggest mistake, was PROBABLY either my MS Optical (it's a good mouse, no questions there, but it cost quite a bit), and this 3com 56k hardware PCI modem..  
I was told it's full duplex, but it's NOT!  *(%#*  I can't even replace it, so I have to wait to sell it, or buy broadband (if/when it comes out here).
otherwise, all my decisions were great, met with varying degrees of speed increases on the computer.